LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA 


f.  t 


LEAC  HING 


GOLD  AND  SILVER  ORES. 


THE  PLATTNER  AND  KISS  PROCESSES, 


A    PRACTICAL   TREATISE 


CHARLES     HOWARD    AARON, 


ILLUSTRATED. 


AND    SOLD   BY   A.    J.    LEARY,    STATIONER, 

402  &  404  Sansome  Street,  San  Francisco. 


>~v 

__pFJTHE_  __  \ 

UNIVERSITY  } 

J 


OF 


SAN 

1..M1HY     &     BAIBD,rvSTEAM    BOOK    AND   JOB    PRINTERS,     419    SACRAMENTO    ST. 

1881. 


. 


Entered  according  to  Act  of  Congress,  in  the  year  1881, 

BY  C.  H.  AARON, 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 


CONTENTS. 


I'AGK. 

Preface 5 

Introduction (.) 

Roasting 15 

Oxidizing  roast 16 

Dead  roast 16 

Chloridizing  roast 17 

Apparatus 21 

Roasting  furnaces 21 

Reverberatory  furnace 22 

Furnace  tools 30 

Crosby's  furnace 80 

Leaching  vat 31 

Suction  pipe 32 

Vent  pipe 33 

Sieve 34 

Precipitating  vat 35 

Troughs 36 

Well. 36 

Pumps 36 

Filters 36 

Press 37 

Chlorine  Generator 37 

Wash-bottle 39 

Special  Directions  for  working — 

A.  Concentrated  pyrites  containing  gold 41 

Roasting , 43 

*  Charging  the  vat 4& 

Chlorination 49 

Making  chlorine 51 

Leaching  the  gold 53 

Precipitating  the  gold 57 

Iron  sulphate  solution 59 

Collecting  the  gold 60 

Washing  the  gold 61 

Drying  the  gold 62 

Melting  the  gold 62 

B.  Concentrated  pyrites  containing  gold  and  silver 65 

Roasting 65 

Leaching  the  silver 67 

Precipitation  of  silver 70 

Collecting  the  precipitate 73 

Roasting  the  precipitate 73 

Melting  the  silver 73 

C.  Concentrations  containing  silver,  but  little  or  no  gold 75 

Roasting 75 

Washing  the  ore 77 

D.  Concentrations  rich  in  gold  and  silver,  and  containing  lead,  &c. .  79 

E.  Unconcentrated  ores ' 80 

F.  Ores  containing  coarse  gold 82 

Calcium  polysulphide 83 

Calcium  hyposulphite 85 

Working  test 86 

Change  in  weight 91 

Loss  in  roasting 92 

Solubility  assay 93 

Plan  of  works 94 

Assaying  concentrations,  &c , .  .  .  97 


132994 


CONTENTS — CONTINUED. 

Addenda—  PAGE- 

Flue  covering • 105 

Filters 105 

Copper 106 

Means  of  drawing  liquid  from  precipitating  vats 106 

Recovery  of  gold 107 

Generators 108 

Wash- bottles 108 

Sifting  ore 1 10 

Cost  of  Acid HO 

Salt  manganese  and  acid Ill 

Assay  of  salt 112 

Assay  of  manganese 114 

Surplus  chlorine   117 

Precipitating  gold 11 

Suspended  gold 11 

Precipitants  for  gold 119 

Sand  in  gold  melting 120 

Drying  chamber 12 

Volatilization  of  gold 121 

Solution  of  silver  in  hypo 124 

Waste  of  sulphur 125 

Recovery  of  sulphur 126 

Matte  from  the  silver 127 

Melting  furnace 128 

Sodium  Hyposulphite .  131 

The  "  chlorination  assay  " 132 

Chlorination  tailings 135 

Value  of  bars * 137 

Chlorine 138 

Plattner's  process 1 40 

The  Kiss  process 142 

The  Bruckner  furnace 143 

The  Brunton  furnace 145 

The  Pacific  chloridizing  furnace ". . . .  145 

The  White  furnace 146 

The  Howell  White  furnace 147 

The  Thompson-White  furnace :    148 

The  O'Hara  furnace 155 

The  Stetefeldt  furnace 156 

Remarks  on  furnaces 161 

LIST  OF  ILLUSTRATIONS. 

Reverberatory  furnace,  horizontal  section 21 

vertical  "        21 

Leaching  vat 32 

Suction  pipe 33 

Precipitating  vat 36 

Chlorine  generator  and  wash-bottle 37 

Generator  cover 3D 

Working  test  apparatus 87 

Plan  of  works 94 

Flue  covering ]  05 

Manganese  assay  apparatus 1J4 

Melting  furnace 128 

The  Bruckner  furnace 143 

The  Brunton  furnace 145 

The  Thompson-White  furnace 149 

The  Stetefeldt  furnace   158 


ffr,       - 


PREFACE. 

0 

This  book  is  written  in  the  endeavor  to  supply,  in 
some  small  degree,  a  want  which  is  severely  felt  on  this 
coast,  namely,  that  of  plain,  practical  books  on  metal- 
lurgy. In  the  standard  works  on  this  subject,  especially 
in  regard  to  gold  and  silver,  there  is  a  great  lack  of 
those  practical  details  which  are  so  essential  to  the 
success  of  the  operator,  while  some  of  them  are  char- 
acterized by  a  display  of  scientific  lore  which  is  very 
discouraging  to  those  whose  preliminary  education  does 
not  enable  them  to  understand  it. 

This  condition  of  affairs-  is  probably  due,  in  part,  to 
the  circumstance  that  books  are  less  often  written  by  prac- 
tical workers  in  this  branch  than  by  scientific  gentlemen 
who  obtain  such  practical  details  as  they  do  give  us, 
not  from  their  own  experience,  but  by  inquiry  and 
observation,  more  or  less  extensive.  It  is  also  in  part 
owing  to  the  fact  that  in  Europe,  where  most  of  the 
works  alluded  to  were  written,  there  are  fewer  men  who 
are  called  on  to  conduct  metallurgical  operations  with- 
out previous  apprenticeship  to  the  business. 

The  processes  selected  for  description,  namely,  the 
Plattner  for  gold,  and  the  Kiss  modification  of  the 
Patera  for  silver,  are  those  which  seem  the  best  adapted 
in  general  to  our  wants;  the  first,  for  the  sufficient  rea- 
son that  it  is  the  only  available  process  for  the  extrac- 
tion of  gold  by  lixiviation;  the.  second,  because  it  is  more 
convenient,  and  requires  a  less  extensive  plant  than  the 


6  PREFACE. 

Augustin  process,  which  depends  upon  dissolving  silver 
chloride  by  means  of  a  hot  solution  of  common  salt, 
while  the  Ziervogel  process,  depending  on  the  forma- 
tion of  silver  sulphate,  which  is  extracted  by  means  of 
hot  water,  is  only  adapted  to  the  treatment  of  matte. 

The  Hunt  &  Douglass  silver  copper  process  is  a 
method  of  lixiviation  which  has  much  to  commend  it, 
but  its  mode  of  operation  and  field  of  adaptability  are 
so  distinct  that  it  will  more  properly  form  the  subject  of 
a  separate  treatise. 

In  the  arrangement  of  the  book,  the  author  endeav- 
ors to  make  the  necessary  explanations  and  practical 
directions  as  simple  and  straightforward  as  possible, 
while  matter  which,  however  interesting  or  instructive, 
is  not  essential,  appears  toward  the  end,  in  a  separate 
division. 

While  it  is  deemed  necessary  to  give  an  outline  of 
the  rationale  of  the  different  operations  describejl,  it  is 
also  thought  desirable  to  avoid,  if  possible,  the  use  of 
terms  which  might  be  in  conflict  with  either  the  old  or 
the  new  systems  of  notation.  Thus,  "sodium  sulphate," 
though  implying  a  departure  from  the  still  older  binary 
system,  in  which  the  formula  for  the  salt  was 
Na  O  S  O3,  and  in  which  it  was  regarded  as  a  sulphate 
of  oxide  of  sodium,  and  called  sulphate  of  soda,  is,  not- 
withstanding, compatible  with  the  use  of  the  old  atomic 
weights,  and  represents  a  view  of  molecular  constitu- 
tion which  antedates,  by  several  years,  the  general 
adoption  by  chemists  of  the  new  weights. 

It  is  with  this  intention  that  the  term  sulphur  oxide 
is  used,  in  preference  to  either  sulphuric  and  sulphurous 
acid,  or  anhydride,  in  speaking  of  the  products  of  the 


PREFACE.  7 

combustion  of  sulphur,  and  the  formation  of  metal  sul- 
phates; for,  while  strictly  accurate,  and  sufficiently  pre- 
cise for  the  purpose,  it  is  the  only  intermediate  term 
which  could  be  used  as  applicable  to  either  of  the  sys- 
tems of  notation. 

The  statement  met  with  in  every  work  on  the  sub- 
ject, that  "sulphuric  acid,"  by  which  must,  of  course, 
be  understood  "  sulphuric  anhydride,"  acts  directly  on 
sodium  chloride,  with  evolution  of  chlorine,  seems, 
while  doubtless  true,  to  require  more  explanation  than 
is  usually  given.  It  may  be  that  air  takes  a  part  in  the 
reaction,  by  supplying  the  oxygen  neceessary  for  the  for- 
mation of  sodium  sulphate,  but  it  appears  to  the  writer 
that  a  clue  to  the  true  explanation  is  furnished  by  Brande's 
statement  that  sulphuric  anhydride  is  decomposed  by  heat 
into  sulphurous  anhydride  and  oxygen.  The  decompo- 
sition is  probably  assisted  by  the  affinities  of  the 
sodium  in  the  gaseous  sodium  chloride.  In  this  view 
the  reaction  would  be 

Na  Cl  +  2  S  03=Na  S  04  +  S  02  +  C1, 
(2  Na  Cl  +  2  S  03=Na2  S  04  +  S  0.2  +  C12) 

which  can  take  place  within  the  roasting  mass,  where 
air  can  have  little  to  do  with  it,  as  well  as  in  the  atmo- 
sphere above  the  ore,  the  sulphuric  anhydride  being 
furnished  by  the  decomposing  metal  sulphates,  under 
the  influence  of  heat,  and  the  nascent  chlorine  having 
the  best  opportunity  to  act  on  remaining  sulphides. 

Chlorine  which  may  be  evolved,  or  may  rise,  above 
the  surface  of  the  ore  will,  in  presence  of  sulphurous 
anhydride  and  steam,  which  latter  must  be  produced 
whenever  fresh  fuel  (wood  or  coal)  is  introduced, 


8  PREFACE. 

form  hydrochloric  a,cid,  with  reproduction  of  sulphuric 
anhydride. 

For  valuable  assistance  in  the  literary  part  of  the 
work  the  author  is  indebted  to  his  friend,  Professor 
John  Calvert,  of  the  California  College  of  Pharmacy, 
San  Francisco.  The  works  which  have  been  consulted 
comprise  those  of  Regnault,  Cooke,  Abell  and  Bloxham, 
Ure,  and  Kustel,  as  well  as  Lippincott's  Encyclopedia 
of  Chemistry. 

While  the  author  has  not  succeeded  in  entirely  satis- 
fying himself,  he  ventures  to  hope  that  the  book  will 
be  found  useful  by  those  who  may  have  occasion  for  it. 


INTRODUCTION 


1.  Leaching,  or  lixiviation,  originally  meant  the  ex- 
traction of  alkaline  salts  from  ashes,  by  pouring  water 
on  them.  The  resulting  liquid  was  called  a  leach, 
lixivium,  or  lye.  In  metallurgy,  at  the  present  day, 
leaching  means  the  extraction  of  metal  salts  from  ores, 
by  means  of  a  watery  solvent.  The  solution  so  ob- 
tained is  called  the  leach  or  lixivium.  Leaching  may 
be  done  in  several  ways — by  filtration,  by  decantation, 
or  by  flowing. 

2:  Filtration  may  be  upward  or  downward ;  the 
solvent  is  passed  through  the  prepared  ore  and  through 
a  filter  which  retains  all  solid  matter. 

3.  Decantation  is  drawing  or  pouring  off  the  solu- 
tion obtained  by  mixing  the  solvent  with  the  ore,  after 
allowing  the  solid  matters  to  subside. 

4.  Flowing  is  allowing  a  stream  of  the  solvent  to 
flow  continuously  into  the  lower  part,  and  out  of  4the 
upper  part  of  a  vessel  containing  the  ore.     The  latter 
is  usually  kept  suspended  in  the  liquid  by  gentle  stir- 
ring, and  the  vessel  is  so  deep  that  only  clear,  or  nearly 
clear  liquid  rises  to  the  outlet. 

5.  Ores  are  usually  leached  for  gold  and  silver  by 
downward  filtration. 

6.  It  is  necessary  that  the  metals  be  combined  with 
some  substance  which  renders  them  soluble  in  the  liquid 
used.     For  gold  and  silver,  chlorine  is  the  most  suitable 


10  .  INTRODUCTION. 

substance  for  this  purpose.  In  order,  then,  to  extract 
gold  and  silver  from  ores  by  leaching,  these  metals  are 
combined  with  chlorine;  the  resulting  compounds,  or 
metal  salts,  are  dissolved,  and  the  leach  is  separated 
from  the  undissolved.  matter  by  filtration.  The  metals 
are  then  separated  from  the  leach  by  precipitation. 

7.  Chemical  combination  differs  from  mere  mixture, 
or  mechanical  combination.  When  two  or  more  sub- 
stances are  merely  mixed,  each  remains  the  same  as  it 
was  before,  and  may  be  separated  from  the  others  with- 
out having  undergone  any  alteration  of  its  properties; 
but  when  they  are  chemically  combined,  they  unite  to 
form  a  substance  which  usually  differs  from  any  one, 
and  from  all  of  the  original  components — a  substance 
which  is  the  same  throughout,  or  homogeneous,  and 
from  which  the  components  can  only  be  recovered  by 
chemical  action.  Thus  gold  and  chlorine  might,  under 
certain  conditions,  be  mixed,  and  again  separated  un- 
changed, by  a  current  of  air;  in  the  interval  the  gold 
would  remain  a  metal,  and  the  chlorine  a  gas.  If  com- 
bined, gold  chloride  would  be  formed,  which  is  neither 
a  metal  nor  a  gas.  It  bears  no  resemblance,  in  ap- 
pearance or  properties,  to  either  gold  or  chlorine  ;  nor 
caii  either  of  those  substances  be  obtained  from  it  by 
any  merely  mechanical  process  of  separation. 

8.  Solution  also  differs  from  mixture;  the  difference 
is  best  explained  by  an  example.  Sand,  clay,  or  gold 
powder  can  be  mixed  with  water,  but  not  dissolved  in 
it.  They  may  remain  a  long  time  suspended,  but  will 
ultimately  settle,  or  may  be  at  once  separated  from  the 
water  by  filtering;  while  sugar,  salt,  or  gold  chloride 
will  dissolve  in  water,  will  not  settle,  and  will  pass  with 


INTRODUCTION.  1 1 

the  water  through  a  filter,  having  in  the  act  of  dissolv- 
ing become  a  liquid,  which  the  other  substances,  not 
dissolving,  did  not. 

9.  Precipitation  means  throwing  down.  It  is 
effected  by  adding  to  a  solution  a  substance,  either  solid 
or  liquid,  which  acts  chemically,  and  causes  the  dis- 
solved substance,  or  some  of  its  components,  to  become 
insoluble  in  the  liquid;  or,  so  changes  the  liquid  as  to 
render  it  incapable  of  dissolving  the  substance,  which 
is  therefore  thrown  down,  or  precipitated.  An  exam- 
ple of  the  first  kind  of  precipitation  is  seen  when  a  drop 
of  muriatic  acid  is  added  to  a  solution  of  silver  nitrate. 
Silver  chloride  is  formed,  which,  being  insoluble  in  the 
liquid,  separates  in  the  solid  state.  If  this  silver  chlo- 
ride be  placed  in  hot  brine,  it  will  be  dissolved,  and  will 
be  again  thrown  down.on  the  addition  of  sulphuric  acid, 
which  so  changes  the  brine  as  to  render  it  incapable  of 
dissolving  silver  chloride.  This  is  the  second  kind  of 
precipitation. 

Precipitation  may  also  be  caused  by  a  change  of 
temperature.  Thus,  if  the  hot  brine  in  which  the  silver 
chloride  was  dissolved  were  allowed  to  become  cool, 
the  silver  chloride  would,  unless  in  very  small  quan- 
tity, be  precipitated,  because  cold  brine  cannot  dis- 
solve so  much  as  when  hot.  Again,  as  any  solvent  can 
only  dissolve  a  certain  quantity  of  a  substance,  it  fol- 
lows that  if  a  saturated  solution  be  exposed  to  evapo- 
ration, the  dissolved  substance,  not  evaporating,  must  be 
thrown  down  in  proportion  to  the  diminution  in  quan- 
tity of  the  solvent.  In  the  latter  two  cases  the  effect 
is  generally  called  crystallization,  or  deposition,  rather 
than  precipitation.  A  substance  which  causes  precipi- 


12  INTRODUCTION. 

tation,  when  added  to  a  solution,  is  called  a  precipitant. 

10.  Chlorine  is  a  greenish  gas,  and  is  usually  pro- 
duced from  common  salt.      When  metals  are  combined 
with  chlorine,  the  resulting  compounds  are  metal  chlo- 
rides, and  are  distinguished  by  the  names  of  the  respect- 
ive metals,  as  gold  chloride,  silver  chloride,  and  further, 
by  the  prefixes  sub,  or  di,  proto,  bi,  ter,  tetra,  penta,  as 
copper  chloride,  copper  protochloride,   mercury  proto- 
chloride,    and    bichloride,    etc.,    representing    different 
proportions  of  chlorine   combined  with   the  respective 
metals.     The  terms  sesqui   and   per,  are  also   used   to 
designate  certain  ratios  of  combination. 

11.  Gold  terchloride,   for  lixiviation,  usually  called 
simply  gold  chloride,  is  made  by  exposing  the  pulver- 
ized ore,  containing  the  metal  in  small  particles,  to  the 
action  of  chlorine    and  moisture.      It  is   extracted  by 
leaching  with  cold  water,:in  which  it  dissolves  readily, 
and  the  gold  is  precipitated  in  the  metallic  state,   as  a 
brown  powder,  by  a  solution  of  iron  sulphate,  known  in 
commerce  as  copperas,  or  green  vitriol,  which  takes  to 
itself  the  chlorine,  and  leaves  the  gold  insoluble.     The 
metal  is  collected,  washed,  dried,  melted,  and  cast  as  a 
bar  or  ingot. 

12.  If  the  rock,  or  ore  containing  the  gold,  is  free 
from  opposing  substances,  it  may  be  chlorinated  without 
being  roasted;  but  in  general,  ores   which   are   treated 
by  lixiviation  contain  the  gold  so  combined,  or  mixed 
with  other  substances,   that  a  preliminary  roasting  is 
necessary. 

13.  Silver  chloride  is  made,  for  lixiviation,  by  means 
of  heat,  in  a  roasting  furnace,  is  extracted  by  leaching 
the  ore  with  a  solution  of  calcium  hyposulphite,  being 


INTRODUCTION.  13 

insoluble  in  simple  water,  and  the  silver  is  precipitated 
as  silver  sulphide,  by  a  solution  of  calcium  polysulphide. 
The  precipitated  sulphide,  in  the  form  of  a  black  mud, 
is  collected,  washed,  dried,  roasted,  and  melted  with  an 
addition  of  scrap-iron,  which  takes  the  sulphur  remain- 
ing after  the  roasting,  and  sets  the  silver  free. 

14.  Silver  sometimes  exists  naturally  combined  with 
chlorine,  in  ore,  and  is  then  soluble  without  roasting; 
but  in  general  it  is  combined  with  antimony,  sulphur  or 
arsenic,  or  with  base  metal  sulphides,  oxides,  etc.,  and 
then  roasting  is  necessary. 


ROASTING. 


15.  As  a  metal  chloride  is  a  compound  of  a  metal 
with  chlorine,  so  a  metal  oxide  is  a  compound  of  a  metal 
with  oxygen,  and   a   metal   sulphide,  or   sulphuret,  is  a 
metal  combined  with  sulphur,  while  a  metal  sulphate  is 
a  metal  combined  with  both  oxygen  and  sulphur — that 
is,  a  metal  oxide  with  a  sulphur  oxide;  the  latter  being 
the  same  which,  when  combined  with  a  certain  propor- 
tion of  water,   is  called  sulphuric  acid,  or   oil  of  vitriol. 
Tfie  metal  oxides,  sulphides,  and  sulphates   are   distin- 
guished irl  the  same  way  as  the  chlorides. 

16.  The  purpose  and  effect  of  roasting  ore  for  lixi- 
viation  is,  as  to  gold,  to  burn  all  base  metals,   sulphur, 
and    other  substances,   such   as   arsenic,  antimony,  and 
tellurium,  and   either  expel   them   by   volatilization,  or 
leave  them  in  such  condition  as  to  be  harmless  in  the 
chlorination  of  the  gold,  and,  as  to  silver,  to  change  its 
condition  in  the  ore,  from  various  insoluble  compounds, 
into  soluble  silver  chloride. 

17.  In  order  that  roasting  may  be  effective,  the  ore 
must  first  be  crushed  to  powder.     The   most  suitable 
degree    of    comminution    must   be   found  by   trial    for 
each  particular  ore.     The  more  coarsely   it  is   crushed, 
consistently  with  good   roasting,  the   more   easily   is   it 
leached.     A  powder  which  will  pass  through  wire  gauze 
of  40  meshes  to  the  running  inch  is   fine   enough,  and 
in  some  cases,  a  sieve  of  20  meshes  to  the  running  inch 
may  be  used  with  advantage.      For.  crushing   there  is, 


16  ROASTING. 

as  yet,  nothing  better   in  the   market   than   the   stamp 
battery. 

18.  Oxidizing  Roast. — The  crushed  ore  is   exposed 
to  heat,  with  abundant  access  of  air.     The  metal  sul- 
phides take  fire  and  burn,  both  metal  and  sulphur  being 
oxidized  by  combining  with   oxygen   from   the  air.     A 
part  of  the  oxidized  sulphur  flies  off  with  the  well  known 
sulphurous  smell.      Another  part  combines  with  a  por- 
tion   of  the   oxidized    metal,   forming   metal   sulphate. 
The  rest  of  the  metal  remains  as  oxide,  except  silver, 
which,  if  not  converted  into  sulphate,  becomes  metallic. 
In  this    way  iron,  copper,    zinc,   and  lead   sulphides  are 
changed,  partly  into  the  respective  sulphates,  and  partly 
into  oxides.    Nearly  the  whole  of  the  silver  is  converted 
into  sulphate,  or    reduced  to  the   metallic   state ;    gold 
remains  unchanged.    Antimony  and  arsenic  are  oxidized, 
and  partly   fly  off,   while   a  part   remains,    to  combine 
with  metal  oxides,  forming  antimonates  and  arsenates, 
much  in  the  way  in  which  sulphur  makes  sulphates.     An 
oxidizing  roast  is  a  roast  so  conducted  that  the  gold  is 
metallic;  the  silver  is  either  metallic  or  in  the  form  of 
sulphate,  and  the  base  metals  are  converted   into  sul- 
phates or  oxides. 

19.  Dead  Roast. — Under  an  increase  of  heat,  some 
of  the  metal  sulphates  which  were  formed  during  the 
oxidation  are  decomposed;    sulphur  oxide  flies  off,  and 
metal  oxide  remains,  although  some  of  the  metal  oxides 
also  volatilize  to  some  extent.    The  order  in  which  some 
of  the  principal  sulphates  are  decomposed  is,  iron,  cop- 
per, silver;  the  last  requiring  a  very  high  heat.      Lead 
sulphate  is  not  decomposed,  nor  is  it  usual  to  push  the 
heat  so  far  as  to  decompose  silver  sulphate.     A  dead 


ROASTING.  17 

roast  is  an  oxidizing  roast,  carried  forward  to  decompo- 
sition of  iron  and  copper  sulphates. 

20.  Chloridizing    Roast. — At   the    commencement 
this  is  the  same  as  an  oxidizing  roast;  but  salt  is  mixed 
with  the  ore,  either  at  the  time  of  charging  the  furnace 
or  at   a  certain  stage  of  the   operation.     The  quantity 
of  salt  used  depends  on  circumstances,  and  varies  from 
one  to  twenty  per  cent,  of  the  weight  of  the  ore. 

21.  Salt  is  a  compound  of  the  metal   sodium  with 
chlorine,  and  is  the  cheapest  source  of  chlorine.     The 
chlorine  of  the  salt  is  transferred,  under  the  action  of 
heat,  from  the  sodium  to  the  other  metals,  by  a  variety 
of  Agencies,  chiefly  by  means  of  sulphur  and  oxygen, 
for  which  the  sodium  has  a  greater  affinity,  whence  it 
happens  that,  when  another  metal  sulphate  is  heated  in 
contact  with  sodium  chloride,  an  exchange  takes  place, 
the  sodium  takes  the  sulphur  and   oxygen,   and  forms 
sodium  sulphate;  the  other  metal  takes  the  chlorine,  and 
forms  a  chloride.      In   this  way,  iron,  copper,  zinc,  lead, 
and  silver  sulphates  form  chlorides,  while  a  correspond*- 
ing  proportion  of  salt  forms  sodium  sulphate.     For  this 
reason,  sulphur    is    necessary   in    a    chloridizing  roast, 
since  without  it  sulphates  cannot  exist. 

22.  The  higher  sulphur  oxide,  formerly  called  dry 
sulphuric  acid,  but  now  known  by  the  name  of  sulphu- 
ric anhydride,  also  plays  a  prominent  part  in  the  de- 
composition of  the  salt  and  the  evolution  of   chlorine. 
The  latter  acts  upon  any  remaining  sulphides,  and  to 
some  extent  on  oxides,  converting  them  into  chlorides. 
It  also  acts  on  metallic  silver. 

23.  Among  other  agencies  involved  in  the  formation 
of  metal  chlorides,  is  that  of  steam,  from  burning  fuel. 


18  ROASTING. 

Steam,  in  contact  with  salt  and  quartz,  at  a  red  heat, 
produces  hydrochloric  acid,  which  assists  in  the  work. 
It  also  decomposes  some  of  the  base  chlorides,  es- 
pecially the  volatile  ones,  thus  giving  the  silver  the 
benefit  of  their  chlorine.  For  this  reason,  steam  is  some- 
times, in  the  case  of  rich  ores,  admitted  to  the  roasting 
chamber  by  means  of  a  perforated  pipe  laid  in  the  fire- 
wall, which  is  made  hollow,  with  openings  on  the 
side  next  to  the  ore.  This,  however,  causes  an  in- 
creased consumption  of  fuel. 

24.  As  the  heat  still  increases,  the  base  metal  chlo- 
rides are  decomposed,  just  as  the  sulphates  are  decom- 
posed in  the  dead  roast.     They  give  off  the  whole,  or 
a^  part  of  their  chlorine,  remaining,  or  volatilizing,   as 
chlorides  of  a  lower  degree,  or  taking  oxygen  from  the 
air  and  becoming  oxychlorides,  or  oxides.     Silver  chlo- 
ride is  not  decomposed  by  heat. 

25.  Iron    perchloride,    formed    quite    early    in    the 
roasting,   is  volatile,   and  some  of  it  flies  away,  while 
another  part,  giving  off  chlorine,  is  reduced  to  proto- 
chloride,  and  this  again,  losing  the  remaining  chlorine, 
takes  oxygen  from   the  air,  and  forms  iron   peroxide, 
which  remains  in  the  ore. 

26.  Copper  protochloride  gives  off  half  its  chlorine, 
becoming  dichloride,  which  volatilizes  to  some  extent, 
imparting  a  deep  blue  color  to  the  flames. 

27.  Lead  sulphate  requires  a   rather  high   heat  to 
convert  it  into  chloride,  so  that  it  remains  in  part,  some- 
times wholly,  unchanged.     The  chloride  gives  off  some 
chlorine  and  takes  oxygen,  becoming  oxychloride. 

28.  Zinc  volatilizes  partly,  in  some  form,  and  pro- 
duces in  the  flues  hard  concretions  of  oxide,  or  carbon- 


ROASTING.     •  19 

ate,  which  must  be  removed  from  time  to  time.     The 
oxide  is  quite  stable. 

29.  Antimony  and  arsenic  form  volatile  chlorides  as 
well  as   oxides,   which,    to   a   great  extent,  go   up    the 
chimney. 

30.  Gold  forms,  at  a  very  low  heat,  a  peculiar  chlo- 
ride which   decomposes  at   a   higher  temperature,  and 
then   remains   metallic,  except  as   a  portion  of  it  may 
be  again  chloridized,  in  the  same  form,  by  chlorine  from 
decomposing  base  chlorides,  during  the  cooling  of  the 
ore,  after  being  withdrawn  from  the  furnace.      The  gold 
chloride  formed  in  roasting  contains  less  chlorine  than 
jhat  formed  by  the  cold  gas,  and  is  not  soluble  in  water, 
but  dissolves  in  the  solvent  used  for  the  silver  leaching. 
The  formation  of  this  compound  cannot  be  relied  on 
as  a  process  for  extracting  gold. 

31.  The   presence    of  lead   is    disadvantageous  for 
the  roasting,  because  its  compounds  melt  too  easily,  and 
because  the  oxide  and  chloride  volatilize,  to  the  injury 
of  the  workman's  health ;  and  for  the  leaching,  because 
the  sulphate  and  chloride  are  soluble  in  the  silver  leach, 
and  the  sulphate  cannot  be   removed  from  the  ore  by 
washing  with  water;  as,  however,  the  chloride  is  soluble 
in  hot  water,  it  is  preferable  to  the  sulphate,  as  it  can  be 
removed  from  the  ore  before  the  silver  extraction  be- 
gins. 

32.  Silver  chloride  is  not  very  volatile  by  itself,  but 
in  some  cases  becomes  so,  apparently  from  the 'influence 
of  base  metal  chlorides,  notably  that  of  iron    perchlo- 
ride,  when  too  much  heat  is  used  early  in  the  roasting. 
Antimony  and  zinc  also  tend  to  cause  volatilization  of 
silver;  so  as   it  does  not  require   a  very  high  heat  to 


20  ROASTING. 

form  the  silver  chloride,  the  roasting  is  conducted,  not 
only  with  a  very  low  heat  at  the  beginning,  but  without 
an  extremely  high  temperature  at  any  time,  and  even  a 
moderately  high  degree  is  maintained  for  a  short  time 
only  towards  the  end.  A  chloridizing  roast  is  a  roast 
which,  beginning  with  oxidation,  ends  by  leaving,  as 
nearly  as  possible,  all  the  silver  in  the  form  of  chloride 
in  the  ore.  I 


Plate  I. 


Plata  II. 


o 


Q 


APPARATUS. 


33.     ROASTING  FURNACES — The  essential  condition 
of  roasting  pulverized  ore  is,  that  every  particle  shall  be 
exposed  to  the  action  of  heated  air  until  certain  chemi- 
cal changes   are   effected,  after   which   heat  alone   Will 
complete  the  operation.      This  condition  is  fulfilled  in 
the    reverberatory    furnace,    in    which  a    layer    of  ore 
of  a  certain  thickness    is    acted  on    by    a    current    of 
heated  ^air   from   a  fire.     The   surface   of   the  layer  is 
renewed    from    time    to    time    by    stirring    the    mass 
by  means  of  implements   operated   by   hand.     As  stir- 
ring by  hand  power  is  laborious  and  expensive,  various 
means  have  been  devised  to  dispense   with   it,  and  to 
substitute  the  automatic  action  of  machinery,  among 
the  best  of  which  are  the  furnaces  known  as  the  Stete- 
feldt,  Bruckner,  Brunton,  White,  Howell  White,  Pacific, 
and  O'Hara,  each  of  which  has  certain  advantages  over 
the  other,  so  that  a  decided  preference,  under  all  circum- 
stances, can  be  given  to  neither,  and  as  the  reverbera- 
tory is  the  original  of  all,  as  any  kind  of  ore  that  is  fit 
to  be  roasted  can  be  roasted  in  it,  and  as   the   operator 
who  knows  how  to  use  it,  can   easily   adapt   himself  to 
the  others,  a   complete  description   of  its   construction 
and  operation   will  be  given,  but,   as  a   work  of  this 
character  would   be  imperfect  without  some  account  of 
the  mechanical   furnaces  also,  they   will   be  briefly  de- 
scribed in  separate  articles  under  "  Addenda." 


22  APPARATUS FURNACES. 

34.  A  Reverberatory  Furnace  is    simply  an   oven. 
There  is  a  fire-place  at  one  end  and  a  flue  at  the  other, 
and  the  ore  to  be  roasted  is  laid  on  a  horizontal  hearth 
between  them.      In  the  side  walls  are  openings,  which 
admit  air,  and  allow  the  workman  to  turn  the  ore  over, 
from  time  to  time,  with  a  long  hoe,   or  rake.     These 
openings  can  be  closed,  when  necessary,  with  iron  doors. 
The  fuel  must  be  such  as  will  produce  a  flame;  hencej 
wood,  or  flaming  coal  is  suitable. 

35.  Reverberatory  furnaces  are  of   several    kinds; 
the  single,  which  has  but  one  roasting  chamber,    the 
double,   in  which  a  second   roasting  chamber  is   con- 
structed directly  over  the  first,  and  is  worked  with  waste 
heat;   and   the   long  furnace,  which  has  two   or  more 
chambers,  either   in  one  horizontal  plane,  or,  which  is 
better  where  the  ground  is  suitable,  raised  more  or  less 
one  above  another,  in  step  form,   but  not   superposed. 

The  single  hearth  is  wasteful  of  fuel;  the  double 
hearth  is  inconvenient,  so  I  will  describe  a  long  furnace 
with  two  hearths,  represented  by  the  horizontal  section, 
Plate  i,  and  vertical  section,  Plate  2.  If  more  than 
two  hearths  are  required,  which  with  concentrated  sul- 
phurets  may  be  the  case,  a  third  or  fourth  can  be  added, 
but  it  will,  in  general,  be  necessary  to  add  also  an  auxil- 
iary fire-place  to  aid  in  heating  them.  The  capacity  of 
this  furnace  is  three  tons  of  average  silver  ore  per 
twenty-four  hours,  or  from  one  to  one  and  a  half  tons  of 
concentrated  sulphurets  in  the  same  length  of  time. 

36.  The  masonry  may  be  built  entirely  of  common 
bricks;  with  adobes  in  case  of  necessity;  but  it  is  better 
to  make  the  inside  of  the  fire-place,  and  the  arch   over 
it,  of  firebrick.     If  convenient  the  outside  walls  can  be 


APPARATUS-  -FURNACES.  23 

of  any  kind  of  stone,  but,  unless  a  good  firestone  can 
be  procured  for  the  inside  work,  that  must  be  of  brick. 
Lime  mortar  may  be  used  with  advantage  for  the  out- 
side work,  but  all  parts  which  are  exposed  to  much  heat 
must  be  laid  in  clay.  The  brickwork  consists  of  head- 
ers and  stretchers  alternately,  appearances  being  sacri- 
ficed for  the  sake  of  strength.  The  masonry  below  the 
hearth  is  not  solid,  but  the  space  inclosed  by  the  walls 
is  filled  with  sand,  or  with  earth  well  tamped,  and  on 
this  the  hearth,  or  sole,  is  laid,  of  the  hardest  bricks  on 
their  narrow  sides,  without  mortar,  but  afterwards 
grouted. 

37.  The  walls  are  supported  against  the  thrust  of  the 
arch  as  follows.  At  the  points  shown  in  the  diagram  are 
vertical  backstays  or  "buckstays,"  of  wrought  iron,  two 
inches  wide  by  one  and  a  quarter  inch  thick,  and  long 
enough  to  reach  from  below  the  hearth  to  just  above  the 
arched  roof.  Through  holes  punched  in  the  backstays, 
near  the  ends,  project  the  nutted  ends  of  tie  rods  of  ^ 
inch  round  iron.  The  lower  tie  rods,  passing  through 
the  body  of  the  furnace,  below  the  hearth,  and  uniting 
the  lower  ends  of  opposite  backstays,  are  put  in  before 
the  hearth  is  laid.  The  upper  ones  extend  across  the 
furnace  above  the  walls,  uniting  the  upper  ends  of  the 
backstays,  and  are  not  put  in  place  till  after  the  walls 
and  arch  are  laid.  Usually  the  furnace  is  stayed  in  the 
direction  of  its  length,  in  the  same  manner,  except  that 
the  lower  longitudinal  tie  rods  do  not  pass  entirely 
through,  but  are  comparatively  short,  being  securely 
anchored  in  the  body  of  the  furnace,  under  the  hearth. 
If  the  ends  of  the  furnace  are  made  masssive,  these 
ties  may  be  dispensed  with,  especially  if  the  ends 


24  APPARATUS FURNACES. 

are  supported  by  wooden  posts  well  braced.  The  cross 
ties,  which  are  indispensable  in  some  form,  may  be  of 
wood,  uniting  the  upper  ends  of  strong  posts,  the  lower 
ends  ot  which  are  sunk  in  the  ground,  close  to  the  side 
of  the  furnace,  and  which  replace  the  iron  backstays, 
the  objection  being  that  the  posts  cannot  be  set  very 
near  the  doors,  both  on  account  of  being  in  the 
way,  and  because  of  the  heat;  but  near  the  doors  is 
precisely  where  they  are  most  needed.  Cast  iron  ribbed 
backstays  are  also  used,  but  are  liable  to  break. 

38.  When  all  is  ready  for   raising  the   walls  above 
the  hearth,  the  cast  iron  door  frames  are  set  up,  in  the 
middle  of  the  thickness  of  the  wall,  which  should  not 
be  less  than  16  inches  thick,  and  a  stirring-hoe  is  passed 
through    each    of   them   in   succession,    and    its   range 
of  operation  ascertained  by  trial,   and   marked   on  the 
hearth.     The  walls  are  then  built  up  along  the  marks, 
cutting  off   the  corners   of  the  otherwise   rectangular 
hearth,  and  giving  it  the  form  seen  in  the  diagram.    This, 
though  entailing  some  loss  of  space  within  the  furnace, 
is  absolutely  necessary,  in  order  that  every  part  of  the 
hearth  may  be  accessible  with  the  hoe. 

39.  The  door  frames  are  two  feet  long  by  eight  in- 
ches high  in  the   clear,    are  set   two  inches  above   the 
hearth,  and  are  built  into  the  wall  as  solidly  as  possible. 
An  exception  is  made  as  to  the  back  door  on  the  first 
hearth,  when  it  is  to  be  used  for  discharging  the  roasted 
ore.      It  must  then  be  set  flush  with  the  hearth,  and  is 
two  inches  higher  in  the  clear,  to  allow  of  using  a  large 
hoe  for  discharging,  but  when  the  discharge  is  effected 
through  a  trap  in  the  hearth,  this  door  frame  is  the  same 
as  the  others.     The  masonry  is  arched  over  the  frame, 


APPARATUS FURNACES.  25 

and  as  the  wall  at  this  point  is  liable  to  be  rather  thin, 
it  is  a  good  plan  to  arch  the  skewback  a  little,  in  a 
horizontal  plane  inwards,  by  which  the  thrust  of  the 
main  arch  against  this  weak  part  is  lessened,  and  to 
some  extent  transferred  to  the  points  at  each  side, 
where  it  is  received  by  the  backstays  and  tie-rods ; 
notwithstanding  which,  it  is  also  well  to  place  above 
each  door  frame,  outside  of  the  wall,  a  flat  bar  of  iron 
two  inches  wide  and  half  an  inch  thick,  the  ends  of  which 
are  tucked  between  the  adjoining  backstays  and  the 
wall. 

40.  Doors  are  sometimes  made  of  cast    iron,   and 
'pivoted  to  the  frames>  but   sheet   iron   doors  detached 

from  the  frames  answer  very  well,  and  are  furnished 
with  long  handles,  made  of  iron  rods  riveted  to  them  at 
right  angles;  when  in  place  they  rest  against  the  rabbet 
formed  by  the  junction  of  the  frames  with  the  masonry, 
the  projecting  handles  being  supported  by  the  roller  in 
front.  Doors  sliding  vertically  on  the  outside  of  the 
wall  are  very  convenient,  being  counterpoised  by  a 
weight  attached  to  one  end  of  a  rope  which  passes  over 
a  pulley,  the  other  end  being  attached  to  the  door  by  a 
short  chain  or  a  link.  A  slot  in  the  lower  part  of  the 
door  allows  it  to  be  closed  while  the  hoe  rests  on  the 
roller,  the  handle  of  the  hoe  being  supported  hori- 
zontally by  a  hook  depending  from  a  beam  above. 

41.  When   the   walls   are   high   enough   above  the 
hearth,  which  is  17  inches  at  the   points  opposite   the 
highest  part  of  the  arch,  and  not  less  than  eight  inches  at 
the  lowest  points,  the  skewback  is  set  up  with  bricks  on 
end,  the  lower  end  being  cut  to  the   proper  angle,  and 
then  the  walls  are  continued  up,  level  with   the  top  of 


26  APPARATUS — FURNACES. 

the  arch.  All  openings  in  the  walls  are  then  tempo- 
rarily stopped,  and  the  enclosed  space  is  filled  with 
moist  sand,  up  to  the  skewback  along  the  sides  and 
ends,  and  higher  in  the  middle,  and  this  is  carefully 
shaped  to  the  required  form  of  the  furnace  top.  On 
the  sand,  as  a  support,  the  arched  roof  is  laid  dry,  the 
bricks  on  end,  one  course  thick,  working  from  the 
skewback  all  along  on  both  sides,  and  keying  in  the 
centre  line.  All  openings  in  the  arch,  such  as  flue  or 
feed  holes,  are  circular,  formed  with  a  course  of  "rollers." 
When  the  arch  has  been  well  keyed,  and  the  openings 
filled  with  sand,  it  is  wetted  by  pouring  water  on  it,  and 
then  grouted  with  a  mixture  of  clay  and  sand,  thinned 
with  water  so  as  to  run  into  and  fill  all  the  interstices 
between  the  bricks.  The  best  way  to  lay  the  bricks  in 
the  arch  is  the  style  called  u  herring  bone,"  but  it 
requires  well  porportioned  bricks,  of  which  the  width  is 
just  twice  the  thickness,  otherwise  straight  courses  are 
to  be  preferred. 

As  soon  as  this  is  done,  the  backstays  and  the 
upper  tie  rods  are  placed  in  position,  and  all 
the  nuts  tightly  screwed  to  support  the  walls,  yet 
not  so  much  so  as  to  move  them.  The  doors, 
which  were  temporarily  stopped  with  loose  bricks,  or 
pieces  of  board  to  retain  the  sand,  are  opened,  and  the 
sand,  on  which  the  arch  was  laid,  is  drawn  out,  to  allow 
the  arch  to  settle  as  it  dries.  In  a  single  hearth  fur- 
nace, the  arch  has  very  little  spring  transversely,  because 
it  abuts  the  other  way  against  solid  end  walls,  but 
in  a  long  furnace  a  transverse  spring  is  more  neces- 
sary, especially  near  the  junction  of  the  two  hearths, 
where  the  roof  descends  and  rises  again,  so  as  in  fact 


APPARATUS FURNACES.  27 

to  be  an  inverted  arch,  as  to  the  longitudinal  section,  as 
may  be  seen  in  Plate  2,  but,  as  this  is  almost  the  nar- 
rowest part  of  the  furnace,  there  is  no  danger  of  its 
falling,  if  it  has  a  good  spring  crosswise. 

42.  In   building    the   fireplace  many  masons,  very 
improperly,  let  the  bearing  bars  for  the  grates  rest  on  an 
offset  in  the  brickwork,  so  that  though  space  be  left  for 
the  lengthening  of  the  grates  by  expansion  when  heated, 
yet  that  space  is  soon  filled  with  ashes  and  other  debris, 
so  that   the  grates    are  forced   to   bend   or  "  buckle.." 
When  they  become  cool  again  they  shorten  but  do  not 
straighten,  the  spaces  at  the  end,  left  by  their  shrinkage, 
are  refilled,   and,    when  again  expanded  by  heat,    the 
grates  buckle  still  more  and  are  soon  ruined. 

The  end  walls  of  the  ash-pit  should  be  perpendicular, . 
without  offsets;  the  bearing  bars  should  be  well  clear  of 
them,  and  the  ends  of  the  grates  should  also  clear  the 
walls  by  at  least  half  an  inch.  The  space  thus  left  for 
expansion  is  then  bottomless,  and  remains  always 
open,  and  the  grates  remain  straight. 

43.  The  flue-holes  are  connected  by  flues  in  any  con- 
venient way,  with  a  stack  which  is  two  feet  square  inside, 
and  20  to  30  feet  high.      In  some  part   of  the  flue  or 
stack  is  a  damper,  similar  to   that  of  a  stovepipe,  oper- 
ated by  the  roaster  through  the  agency  of  a  cord  or 
wire. 

44.  It  is  desirable  to  utilize  as  much  as  possible  the 
waste  heat  from  the  furnace,  and  it  is  a  good  plan  to  carry 
the  flue  in  front  of  the  stamp  battery,  if  dry  crushing  is 
done,  and  there  enlarge  it  to  form  a  dust  chamber.      The 
top  of  the  chamber  is  of  sheet  or  boiler  iron,  which  forms 
a  drier  on  which   to   dry   the  ore  for  crushing.      Even 


28  APPARATUS FURNACES. 

where  only  concentrated  sulphides  are  treated,  so  that 
no  crushing  is  required,  a  drier  is  convenient,  and  may 
very  properly  be  the  top  of  the  dust  chamber.  The 
walls  are  built  two  bricks  high  above  the  iron  plate,  and 
topped  with  two-inch  plank,  held  down  by  anchor  bolts 
built  into  the  walls.  If,  however,  there  is  a  battery,  the 
side  of  the  drier  next  to  it  is  without  a  wall  above 
the  plate,  which,  if  thin,  is  secured  by  an  anchor  bolted 
iron  strap  along  the  edge. 

45.  If  silver  ore  is  treated,  a  drier  is  necessary  for 
the  precipitate.      It  may  be  made  as  described  above,  to 
be  heated  by   the  waste  heat  from  the  roasting  ore,  by 
steam,  or  by  a  special  fire.     A  small  roasting  furnace  is 
also  requisite  for  roasting  the   dried  precipitate.      It  is 
built  similarly  to  the  large   furnace,  except   that  it  has 
but  a  single  hearth  and  one  working  door.     A  hearth 
containing  36  to  40  square  feet  of  surface,  will  suffice 
for  the  roasting  of  from  one  to  two  thousand  ounces  of 
silver,  in  the  form   of  precipitate,  in  each   twenty-four 
hours. 

46.  It  will  be  observed,  by  those  accustomed  to  fur- 
naces, that  there  are  two  small  innovations  in  the  plan 
given.     Firstly,  the  ash-pit  is  opei^  entirely  across  the 
furnace.     This  gives  the  operator  the  choice  of  leaving  it 
so,  or  of  closing  either  end,  which  is  sometimes  an  advan- 
tage on  account  of  the  draft.      It  is  generally  preferable, 
though  contrary  to  custom,  to  have  the  opening  on  the 
rear  side  of  the  furnace,  that  is  the  side  opposite  to  the 
fire  door,  because  the  cold  air,  entering  under  the  hot- 
ter end   of  the   fireplace,  tends    to    equalize    the    heat. 
Especially  is  this  the  case  when  the  workman    pushes 
the  half  burned  wood  back,  when  introducing  fresh  fuel, 


APPARATUS FURNACES.  29 

instead  of  drawing  it  forward  as  he  should  do.  Secondly, 
the  doors  on  the  first  hearth  are  not  placed  in  the  mid- 
dle of  its  length,  as  is  usual,  but  a  foot  nearer  to  the 
fireplace.  Here  again  the  object  is  to  equalize  the 
heat,  by  causing  the  cold  air  which  enters  by  the  door, 
to  pass  over  the  hotter  portion  of  the  ore  near  the 
fire  wall.  Another  advantage  is  that  the  hearth  is 
made  wider  near  the  fire  wall,  and  narrower  at  the 
other  end,  thus  concentrating  the  heat  toward  the 
part  which  is  farthest  from  the  fire. 

47.  When   a   long  furnace,  which   may  have    any 
required  number  of  hearths,  is  built  on  a  hillside,  it  is 
a  good  plan  to  make  each   successive  hearth   two  feet, 
or  even  more,  higher  than  the  preceding  one,  the  one 
next  to  the  fire-place  being  the  lowest.      By   this   plan 
the  cost   of  grading  is   lessened,  and  the   dropping  of 
the  ore  from  one  hearth   to  the  other  assists  greatly  in 
the  oxidation.     This  is  called  a  "step  furnace." 

48.  Furnaces  are  often  built  with  an  arched  cham- 
ber under  the  first  hearth,  as  shown  by  the  dotted  line 
in  Plate  2.     This  chamber  is  closed  on  the    working 
side   of  the  furnace  and  open  on   the  other,  and  the 
ore  is  discharged  into  it    through  an   opening  about  a 
foot   in  diameter,  in  the  hearth  near  the  working  door. 
The  opening  is  closed   by  an  iron  plate,  which  rests  on 
a  rabbet  a   couple   of   inches    below  the   level   of  the 
hearth,  and   the  depression  thus  formed  is  filled  with 
roasted  ore.     A   small  flue  from  the  chamber,  leading 
through  the  wall  to  the  interior  of  the  furnace,  removes 
the  fumes  rising  from  the  hot  ore,  which  is  not  drawn 
out  of  the  chamber  to  the  cooling  floor  for  some  time. 


30  APPARATUS FURNACES. 

It  is  a  good  arrangement.    The  floor  on  each  side  of  a 
furnace  is  paved  with  bricks  to  a  width  of  14  feet. 

49.  Furnace  Tools. — The  tools  required  for  such  a 
furnace  are:  three  or  four  hoes,  each  fourteen  feet  long; 
a  couple  of  smaller  ones  about  six  feet;  two  spades  not 
shorter  than   the  large  hoes;  a  poker,   which,   if  wood 
is  the   fuel,   should    be  made   like  a   boat-hook.      The 
shanks  of  the  hoes  and  spades  are  of  three-quarters  or 
one   inch    gaspipe,   except    some   three   feet    next  the 
head,  which  is  of  solid  round  iron.     The  heads  are  of 
one-quarter   or   one-half   inch  boiler  iron.      Fo_r  very 
heavy  ores,  containing  arsenic  and  antimony,   cast-iron 
hoe  heads  are  used,  also  rakes.     These  tools  are  repre- 
sented in  Plate  2. 

50.  Crosby  s  Furnace. — At  Nevada  City,    Professor 
Crosby  uses,  in  connection  with   a   reverberatory  fur- 
nace, an  inclined,  rotating,  unlined  iron  cylinder,  which 
receives  the  concentrated  sulphides  at  the   higher  end, 
and  delivers  them  at  the  lower  end,  already  to  a  great 
extent  oxidized,  into  a  chamber  where  they  are  exposed 
to  the  heat  from  the  reverberatory  hearth,   to  which 
they  are  removed  periodically,  in  batches,  and  finished 
under  hand  stirring  with  hoes.     A   fire  is  used  under 
the  cylinder,  to  commence  the  burning  of  the  sulphides, 
after  which  they  continue  burning  without  such   aid, 
combustion  being  supported  by  the   air  which   enters 
through  the  open  upper   end  of  the  inclined  cylinder 
with  the  sulphides,  the  fumes  being  carried  off  at  the 
other  end  by  the  draft  of  the  furnace,  with  which  the 
cylinder  is  in  communication. 

The  sulphides,  thus  burning  spontaneously,  receiving 
an  abundance  of  fresh  air,  being  constantly   moved  by 


APPARATUS VATS.  31 

the  rotation  of  the  cylinder,  and  afterwards  lying  in  the 
furnace,  exposed  to  a  higher  heat  while  accumulating, 
require,  when  transferred  to  the  finishing  hearth,  but  a 
short  time  to  complete  the  roasting.  Thus  three  tons 
of  material  which  requires  24  hours  in  an  ordinary  long 
furnace,  can  be  turned  out  daily  by  the  labor  of  only 
two  men.  Some  power  is  consumed  in  turning  the 
cylinder,  which  however,  when  power  is  not  required 
for  other  purposes,  might  be  had  by  applying  the  waste 
heat  of  the  furnace  to  a  small  steam  or  hot  air  engine. 

51.  Leaching  Vat. — The  leaching  is  done  in  wooden 
tubs,  which  are  coated  inside  with  a  mixture  of  coal 
tar  and  asphalt  melted  together,  and  applied  whilst 
hot.  As  the  chlorination  of  gold  is  also  effected  in  these 
tubs,  they  are  provided  with  covers  when  that  metal  is 
present  in  the  ore.  If  there  is  no  gold,  covers  are  not 
needed,  nor  is  the  coating  of  the  tubs  with  tar  so  neces- 
sary, being  in  fact  inadmissible  if  hot  water  is  to  be 
used  to  wash  the  ore. 

The  side  of  a  leaching  vat  is  either  vertical,  or 
flaired  so  that  the  top  of  the  tub  is  wider  than  the 
bottom.  The  reverse  form  is  not  suitable,  because  the 
ore,  in  settling,  draws  away  from  the  sides,  and  leaves 
a  space,  or,  at  least,  a  greater  looseness,  through  which 
the  chlorine  can  pass  upward,  or  liquids  downward, 
without  passing  through  the  mass.  The  vat  represented 
in  Plate  3,  is  suitable  for  the  treatment  of  ore  con- 
taining both  gold  and  silver.  Its  capacity  is  two  and 
three-quarter  tons  of  roasted  ore. 

The  vats  have  filters  near  the  bottom,  and  rubber 
pipes,  connecting  under  the  filters,  for  the  solution  to 
flow  through  to  the  precipitating  tubs.  For  the  ad- 


32  APPARATUS VATS. 

mission  of  chlorine   a  leaden  nipple  is  inserted  in  the 
side  of  the  vat   immediately  below  the  filter. 

52.  In  some  works  the  vats  are  suspended  on  iron 
gudgeons,  attached  to  their  sides,  in  order  that  they  may 
be  emptied  quickly  by  dumping.      It   is   a  convenient 
arrangement  if  completed  by  having  a  stream  of  water 
in  a    sluice  below,  or    a  tramway,  for   the   removal  of 
tailings.       In    others    the    leaching    vats     themselves 
are  mounted   on   wheels,  and  can  be   trundled    to   the 
dumping  place. 

53.  The    filter    consists   of  a   false  bottom  of  inch 
boards,  through  which   half  inch   holes  are   pierced   at 
intervals  of  about  four  inches.     The   boards   are  laid 
loosely,  with  open   spaces   a  quarter   of  an   inch    wide 
between  and  around  them.     The  false  bottom  rests  on 
strips  of  wood,  by  which  it  is  raised  from  half  an  inch 
to  an    inch    above  the    true    bottom.     As    the    vat   is 
slightly  inclined   toward   the  discharge   side,  to  insure 
complete  draining,  the  strips  are  made   thicker   at   one 
end  than  at  the  other,  so  that  the  false  bottom  is  hori- 
zontal.    They  do  not  touch   the   sides   of  the   vat,  but 
leave  a   space  for  the  flow  of  solution   and  diffusion  of 
chlorine.      On  the  false  bottom  is  a  layer  of  pebbles  as 
small  as  may  be   without  falling  into,  or  through,  the 
holes.     Over  the   pebbles  is   a   sheet   of  burlap,   or  a 
layer  of  old  grain   sacks,  which   are    cheap  and  good 
enough,  as  they   are   soon  destroyed   by   chlorine,   on 
which  account  some  operators  prefer    a  layer  of  fine 
gravel  covered  with  sand. 

54.  Suction  Pipe. — In  cases  of  difficult  leaching,  fil- 
tration may  be  facilitated  by  means  of  a  suction  pipe. 
This  is  simply  the  discharge  pipe  of  the  leaching  vat, 


Plate  III. 


Scale;   Yz  inched  foot. 


APPARATUS VATS. 


33 


made  of  stiff  hose,  or  of  wood,  instead  of  soft  rubber 
as  in  other  cases,  and  extended 
to  a  vertical  depth  of  from  six  to 
twenty-five  feet.  The  hose,  near 
its  lower  end,  is  coiled  once  around, 
as  in  the  accompanying  diagram, 
and  secured  by  a  piece  of  wire;  or, 
a  re-curved  piece  of  lead  pipe  may 
be  inserted  in  the  end  of  the  dis- 
charge pipe,  or  again,  the  end  may 
be  immersed  in  a  cup  of  water, 
although  this  plan  is  less  conven- 
ient than  the  others.  The  object, 
in  either  case,  is  to  prevent  the  en- 
trance of  air. 

55.  Vent  Pipe. — Though  not  the 
general  practice,  it  is  well  to  have  a 
vent  pipe  to  prevent  disturbance,  of 
the  filter  by  the  air  or  gas  beneath 
it,  when  displaced  by  the  entrance 
of  water,  especially  if  the  discharge 

[SUCTION  AND  VENT  PIPES.]  *  <=> 

pipe  is  hung  up,  closed  as  in  the  case  of  using  suction, 
or  occupied  by  the  introduction  of  water  below  the  fil- 
ter, as  in  commencing  the  washing  of  silver  ore.  There 
are  several  methods  of  arranging  a  vent  pipe.  Perhaps 
the  simplest  is  the  following,  represented  by  a  dotted 
line  in  the  preceding  diagram. 

When  the  ore  vat  is  disconnected  from  the  chlorine 
pipe  a  short  piece  of  rubber  tube  is  connected  at  one 
end  with  the  nipple  through  which  the  chlorine  was  in- 
troduced, and  at  the  other  with  the  upper  part  of  the 


34  APPARATUS — VATS. 

vat,  by  being  inserted  tightly  in  a  hole  bored  through  the 
side,  just  below  the  cover.  The  short  tube  may  be 
left  permanently  on  the  lead  nipple,  and  connected  with 
the  chlorine  pipe  when  required,  by  means  of  a  short 
piece  of  lead  pipe,  which  afterwards  serves  also  for  con- 
necting the  tube  with  the  hole  in  the  vat  side. 

Whether  water  be  introduced  from  above  or  below 
the  ore,  the  air  or  gas  beneath  the  filter  will  pass 
through  the  tube,  and  return  to  the  vat  above  the  ore. 
If  the  chlorine  nipple  is  to  be  used  thus  as  a  vent,  it 
should  be  set  in  as  high  as  possible,  consistently  with 
the  delivery  of  the  chlorine  below  the  filter.  A 
special  vent  pipe  may  be  made  by  boring  a  one-quarter 
inch  hole  lengthwise  through  a  strip  of  wood,  and  at- 
taching the  strip  to  the  inside  of  the  vat  by  means  of 
wooden  pins.  It  should  terminate  at  one  end  im- 
mediately below  the  vat  coyer,  and  at  the  other,  beneath 
the  burlap  on  the  gravel.  The  upper  end  must  be 
plugged,  and  a  transverse  hole  bored  to  connect  with 
the  vertical  passage.  This  aperture  must  be  plugged 
during  the  chlorination,  and  opened  when  water  is  ad- 
mitted. 

56.  Sieve. — This  is  made  of  stout  brass  wire,  and 
has  from  four  to  eight  meshes  to  the  running  inch,  It 
is  of  an  oblong  form,  about  two  feet  wide  by  three  feet 
long,  and  is  framed  with  wood.  The  sides  are  six  in- 
ches high,  and  are  prolonged  so  as  to  form  handles  at 
one  end,  like  those  of  a  wheelbarrow,  and  at  the  other^ 
points  of  attachment  for  suspension  ropes  from  a  sup- 
port above.  It  is  operated  by  hand,  being  swung  back 
and  forth,  directly  over  the  vat  which  is  in  course  of 
being  charged,  into  which  the  ore  which  passes  through 


APPARATUS — VATS.  35 

falls,  in  a  loose  and  open  condition,  while  the  lumps  are 
retained. 

57.  Precipitating  Vat. — Figure  i,  Plate  4 — This  is 
also  a  wooden  tub,  and,  if  for  gold,  is  coated  inside  as 
the  leaching  vat.     A    smooth    bottom    is    made    in    it, 
either  by  means  of  a  layer  of  tar   and   asphalt,    melted 
together  in  such  proportions   as  to   harden  on   cooling, 
or  by  a   bed  of  Portland   cement,  which  can  be  shaped 
as  desired,  to  facilitate   the  removal  of  the   precipitate. 
A  precipitating  vat  is  made  wider  at  the  bottom  than  at 
the  top,  in  order  that  the  precipitate   may  not  settle 
upon  the  staves. 

58.  For  drawing  off  the  waste  liquor  after  precipi- 
tation, the  most  convenient,  because  self-acting  arrange- 
ment is  a  piece  of  two  inch   hose,   drawn   water-tight 
through  the  side  of  the  tub  near  the  bottom,  and  long 
enough  on  the  outside  to  lead  to  a  filter,  or  a  settling 
tank,  on  a  lower  level,  and  on  the  inside  to  reach  the 
top  of  the  tub,  where  it  is  secured,  when  not  in  use,  by 
a  wooden  clamp.     On  this  end  is  a  wooden  float  which 
causes  the  hose,  when  in  use,  to  draw   always  from  the 
surface;  also  serving  to  prevent  its  drawing  too   near 
to  the  bottom  so  as  to  cause  a  loss  of  gold.     The  other 
opening,  furnished  with  a  large  wooden  faucet,  is  only 
used  when  collecting  the  precipitate. 

The  silver  precipitating  tubs  must  be  larger,  or 
more  numerous,  than  those  for  gold,  because  the 
volume  of  silver  solution  is  much  the  greater.  The 
size  represented  in  Plate  4,  is  sufficient  for  the  gold 
lixivium  from  one  vat,  such  as  is  shown  in  Plate  3,  but 
both  for  gold  and  for  silver,  extra  vats  are  provided  for 
very  weak  solutions,  drainings,  etc.  The  smaller  vat, 


36  APPARATUS — VATS. 

Figure  2,  Plate  4,  is  to  contain  a  solution  of  iron  sul- 
phate. It  is  provided  with  a  filter,  and  a  discharge 
pipe  which  reaches  to  the  gold  precipitating  tub,  and 
which,  when  not  in  use,  is  turned  up  and  fastened'as  in 
the  figure.  This  vat  is  elevated  so  that  the  precipitant 
may  be  used  with  convenience.  For  silver  a  similar 
vat  contains  the  calcium  polysulphide.  It  does  not 
require  a  filter,  but  the  pipe  is  inserted  a  little  higher* 
to  allow  room  for  sediment. 

59.  Troughs  for  conveying  the   lixivium   from  the 
leaching  vats  to  the   precipitating  tubs,  are   not   built, 
but   hollowed   out   of  timber.       They    are    about    five 
inches  wide  and  four  deep,  and  are  tarred. 

60.  Well. — As  the  silver  leaching  solution,  or   "  hy- 
po," is  not  thrown  away,  but   is  used  again  continually, 
it  is  usual  to  provide  a  well  on  a  lower  level  than   that 
of  the  silver  precipitating  tubs.      A  tub   or   square   vat 
sunk  in  the  ground  answers  the  purpose. 

61.  Pumps. — For  elevating  the  leaching  liquid  from 
the  well  a  wooden  pump  is  used.     The  small   quantity 
of   metal   used   in   its   construction,    for   fastening    the 
valves,  etc.,  is  not  injurious.      In  case,  however,  a  pump 
is  used  to  raise  weak  lixivium  from  the  gold   leeching, 
it  must  be   constructed   entirely   without   metal,  except 
lead,  in  those   parts   which   come   in   contact   with   the 
lixivium.      Rubber  ball  valves  are  best   for  this   pump. 
A  well  may   be   dispensed   with   if  desired,  by   having 
the   discharge    pipes  of  the    silver    precipitating   tubs 
connected  directly  with  the  pump, 

62.  Filters. — To  receive   the   precipitate   from    the 
silver  tub   there  is  a  filter  vat,  either  round   or  square, 
in  which  it  is  drained  and  washed.     The  filter  is   made 


Plate-  IK 


Plate    TT 


K 


APPARATUS-  -GENERATOR.  37 

like  those  in  the  leaching  vats,  except  that,  instead  of 
burlap,  cotton  drilling  is  used.  Filters  for  the  precipi- 
tated gold  are  simple  pointed  bags  made  of  drilling,  or 
sheets  of  drilling  secured  over  the  rims  of  water 
buckets  which  have  plug  holes  near  the  bottoms,  with 
hollow  plugs  through  which  the  filtrate  flows  to  a  re- 
ceptacle beneath.  A  large  tank,  in  which  is  a  filter 
made  of  sand  or  saw  dust,  is  usually  placed  outside 
the  works.  It  is  used  for  filtering  the  liquid  drawn 
from  the  gold  tub  after  the  precipitation  of  the  gold. 

63.  Press. — To  facilitate    the  drying  of  the  silver 
precipitate  it  is  pressed  into  cakes.     The  press  is  simi- 
lar  to   a  cheese  press.      It   is   sometimes   operated   by 
means  of  a  screw,  but  a  weighted  lever  is  better,  be- 
cause self-acting.     A  press   may  be  dispensed  with  if 
the  drying  facilities  are  ample. 

64.  Pipes  and  faucets  must  be  provided  for  the  con- 
veyance of  water  and   hypo  to  the  points  where  they 
are  required.      Iron   pipes   with   brass   faucets   may  be 
used  for  the  hypo.     A  few  paper  buckets  will  be  useful. 

65.  Chlorine   Generator. — Figure   i,    Plate   5,    is  a 
section  of  this  apparatus.      It  is  made  almost  entirely 
of  lead,  sometimes  heavy  sheet,  but  better  cast  lead,  and 
is  arranged  so  as  to  be  heated  from  below,  either  by  a 
special  fire,  or  preferably,  when  convenient,  by  steam. 
If  heated  by  a  fire,   it  stands   on    a  sand  bath,  which 
forms  the  top  of  the  fire  place.      If  by  steam,  the  gene- 
rator itself  forms  the  top  of  an  iron  steam  chest,  being 
supported  on  strips  of  wood,  which  permit  the  steam  to 
circulate  beneath  it. 

66.  The  joints  of  the  lead  work  must  not  be  soldered, 
but  "burned;"  that  is,  joined  with  melted  lead,  by  means 

3 


38  APPARATUS GENERATOR. 

of  a  gas  blow-pipe.  Very  coarse  solder  will,  however, 
answer  for  repairing  it.  Portland  cement  also  answers, 
in  case  of  necessity,  for  stopping  a  leak. 

67.  The  apparatus  consists  of  a  leaden  tub  a,  in 
which  the  materials  are  put,  and  which  is  surrounded 
by  a  water  chamber  b,  also  of  lead,  the  outer  wall-  of 
which  rises  as  high  as  the  top  of  the  cover,  c,  and  in 
which  the  curtain  of  the  cover  rests,  forming  what  is 
called  a  water  joint.  The  water  should  be  six  inches 
deep,  or  more.  The  pipe,  d,  is  for  the  removal  of  spent 
material.  In  the  cover  is  a  central  water-joint  opening, 
through  which  passes  the  stem  of  a  stirrer,  e,  made  of 
iron,  covered  with  lead,  and  to  which  is  attached  a  small 
leaden  bell,  or  curtain,  f,  which,  reaching  near  to  the 
bottom  of  the  water  chamber,  closes  the  opening,  while 
allowing  the  stirrer  to  be  turned  round  by  means  of  the 
cross  bar,  g.  Another  opening,  /z,  which  is  closed  either 
by  a  water-joint  cover,  or,  as  shown  in  the  figure,  by  a 
wooden  plug  wrapped  in  greased  cloth,  serves  for  intro- 
ducing material  without  lifting  the  main  cover.  For 
the  introduction  of  acid,  there  is  a  leaden  pipe,  i,  which 
is  coiled  once  round,  as  shown  in  the  figure,  in  order 
that  the  lower  part  of  the  coil,  remaining  always  full  of 
acid,  may  act  as  a  valve  to  prevent  the  escape  of  the 
.  chlorine.  The  pipe,  k,  is  for  the  exit  of  the  chlorine. 

The  subjoined  diagram  represents  the  cover  in 
a  different  position,  showing  the  lugs  and  the  chain 
sling,  by  which  it  is  raised;  also  a  hook  sustain- 
ing the  stirrer,  which  might  otherwise  injure 
the  cover.  A  lever  or  tackle  is  used  for  the  lift- 


APPARATUS WASH    BOTTLE. 


39 


ing.  For  further  re- 
marks on  generators,  see 
"Addenda,"  near  the  end 
of  this  volume.. 

68.  Wash  Bottle.— 
Figure  2,  Plate  5.  This 
is  a  bell  glass,  made  from 
a  large  bottle,  the  bot- 
tom of  which  is  cut  off. 
It  is  fixed  air-tight,  as 
shown,  in  the  head  of 
a  keg,  or  the  tightly  fit- 
ting cover  of  a  small 
tub.  A  piece  of  pure 
rubber  tube,  /,  which 
is  connected  with  the 
leaden  pipe,  /£,  of  the  generator,  passes  through  the  neck 
of  the  bottle,  and  is  packed  so  as  to  be  air-tight,  with 
oiled  rags  and  putty,  and  terminates  two  or  three  inches 
below  the  surface  of  the  water  with  which  the  tub  or 
keg  is  filled.  The  chlorine,  rising  through  the  water 
into  the  bell,  escapes  through  the  leaden  pipe,  m,  and 
is  conveyed  to  the  chlorinating  vat  by  the  rubber  tube, 
n.  The  pipe,  m,  is  passed,  water-tight,  through  a  short 
piece  of  oiled  rubber  tube  inserted  in  a  hole  bored  in 
the  side  of  the  keg,  and  its  upper  end,  reaching  nearly 
to  the  top  of  the  bell,  and  well  above  the  water,  is  bent 
downward  to  prevent  the  entrance  of  water,  which 
might  occur  in  consequence  of  the  bubbling  up  of  the  gas, 
and  which  would  cause  an  obstruction  in  the  rubber 
tube. 

If  two  vats  are  chlorinated  at  once,  the  rubber  tube, 


40  APPARATUS WASH  BOTTLE. 

;/,  is  connected  with  a  forked  piect±  of  lead  pipe,  each 
branch  of  which  is  connected  with  the  lead  nipple  of  a 
vat  by  a  piece  of  rubber  tube.  The  connections  are 
quickly  made  by  .drawing  the  tightly  fitting  oiled  rub- 
ber tubes  an  inch  on  to  the  pipes. 

69.  All  rubber  tubes  used   for  chlorine  should  be 
oiled  on  the  inside.    It  is  a  valuable  fact,  for  the  knowl- 
edge of  which  I  am  indebted  to  E.  N.  Riotte,  that  oil 
is  a  great  protection    against    the   action   of   chlorine, 
which  forms  with  it  a  white,  waxy  substance.     For  this 
reason,  oil  or  grease  is  an  excellent  material  for  stopping 
small  leaks  in  the  apparatus. 

70.  The  wash  bottle  serves  the  double  purpose  of 
washing  the  gas  to  remove  any  acid  which    may  pass 
over  with  it,  and  of  showing  whether  or  not  the   gene- 
rator is  operating  properly,  by  the  quantity  of  chlorine 
which  is  passing.      The   chlorine  should   rise  through 
the  water  in  a  steady  stream.       If  it  does  not,  the  rea- 
son is  either  that  it  is  not  produced  fast  enough,  or  the 
orifice  of  the  pipe  is  too  large,  which  may  be  remedied 
by  flattening  the  pipe  more  or  less.      Other  forms   of 
wash  bottle  will  be  found  described  under  "Addenda." 


SPECIAL    DIRECTIONS     FOR 
WORKING. 


71.  A. — Concentrated  Pyrites  containing  gold,    biit 
no  silver. — This  material  is  produced  in  the  gold  quartz 
mills,  by  crushing  the  rock  in  a   wet   stamp  battery,  in 
which  the  free  gold   is   amalgamated   with  quicksilver, 
and  passing  the  tailings   over   concentrating    machines, 
by  which  the  sulphides  are  almost  entirely   freed  from 
rock  and   earth.      It  generally  consists   mainly  of  iron 
bisulphide,    called    pyrites,   but   often    contains   copper 
pyrites,  sometimes   lead   and   antimony   sulphides,  etc., 
and   in   other   cases    consists   chiefly   of  arsenical   iron 
pyrites.     Tellurium  is  also  met  with. 

72.  Concentrations    should   be   treated   as  soon   as 
possible  after  production,  or  kept  in  tanks,  under  water, 
for,  if  allowed  to  lie  long  exposed  to  the  weather,  they 
oxidize  spontaneously  to  a  certain  extent,  and  form  hard 
lumps    which    must   be    repulverized    for   roasting,    for 
which    purpose   a   self-feeding   and   discharging  barrel 
pulverizer  is  very  suitable. 

73.  Ores  of  this  class  containing  talc,  or  lime,  re- 
quire the   addition,  during  or  before   the   roasting,   of 
from  one  to  five  per  cent,  of  salt,  to  convert  those  sub- 
stances into  chlorides,  otherwise  they  would  consume  a 
great  deal  of  gas  in  the  subsequent  chlorination   of  the 
gold. 

74.  The  furnace,  if  new,  is  dried  during  five  or  six 
days  with  the  aid  of  a  very  small   fire,   after   which,  or 


42  SPECIAL    DIRECTIONS GOLD. 

if  it  has  been  used  before,  it  is  heated  for  from  eight  to 
twelve  hours,  with  a  gradually  increasing  fire,  but,  for 
this  class  of  ore,  need  not  be  red  hot  before  charging, 
because  there  is  so  much  sulphur  in  the  ore  that  it  soon 
ignites,  and  assists  in  heating  the  furnace.  While  heat- 
ing the  furnace,  a  quantity  of  the  ore  is  dried  on  the 
drier,  being  turned  over  occasionally  with  a  garden  hoe, 
and  a  charge  is  put  into  the  hopper. 

75.  Many  operators  put  too    much    ore  in    the  fur- 
nace, which  increases  the  work  of  the  roasters,  without 
any    corresponding    advantage,    because    the    term    of 
roasting  is  nearly  proportional   to  the   thickness   of  the 
bed  of  ore  on  the  hearth.      I   have   found,  by  repeated 
experiments,  that   from   ten    to   twelve   pounds   to   the 
square  foot  of  hearth  is  enough.      The   charge  for  the 
furnace  described    is,  therefore,  1,000   pounds   on   each 
hearth,  or  a  ton  in  all,  so  the  charge  for   the   hopper  is 
half  a  ton. 

76.  When  the  furnace  is   ready,  a  charge   of  ore  is 
dropped  in  on  the  second  hearth,  and   at   once   moved, 
with  hoe  and  spade,  to  the  first,  and  there  spread  evenly. 
Meanwhile,  a  second   charge   is   put   into  the   hopper, 
dropped  on  the  second  hearth  and  spread.      Care  must 
be   taken    that    none    of  this  charge   falls  on   the   first 
hearth,  for  which  reason  the  second  hearth,  as  may  be 
seen  by  referring   to    Plates    i  and   2,   is   made   a   foot 
longer,  and  the  first  foot  has  a  slight  downward  inclina- 
tion, as  it  is  intended  to  be  left  bare  of  ore   during  the 
roasting,   and    to   act  as   a   partition    between  the   two 
charges. 

This  is  very  important  in  roasting   ore   for   chlorina- 
tion,    because  the  admixture    of  a   little    raw   ore   with 


SPECIAL    DIRECTIONS GOLD.  43 

that  which  is  half  roasted  causes  great  delay  in  finish- 
ing; or,  half  roasted  ore  mixed  with  that  which  is  roasted 
is  injurious  in  the  chlorination.  Some  operators  build 
the  hearths  on  the  same  level,  and  separate  them  by  a 
low  wall,  over  which  the  ore  is  lifted  with  the  spade 
when  transferred  from  the  second  hearth  to  the  first. 

77.  Roasting. — When   the  sulphur  begins  to  burn 
on  the  first  hearth,  the  fire   is   kept  quite  low.     The 
burning  of  the  sulphur  can  be   seen,  even   in  the  day 
time,  if  the  furnace  house  is  dark,  as  it  should  be,  with 
no  cracks  or  windows  through  which  the  sun  can  shine, 
a  point  of  some   importance,  which  is  not  sufficiently 
attended  to.     It  is  difficult  to  properly  regulate  the  heat 
in  full  day  light,  but  it  is  even  worse  if  the  sun  shines 
in  through  chinks  or  windows,  so  that  an  open  shed  is 
better  than  an  imperfectly  inclosed  room. 

78.  Continuous   stirring  of  the  ore   is  useless,   for 
there  is  a  certain  quantity  of  sulphur   to   be    burned, 
which  requires  a  certain  quantity  of  air,  and  there  is  no 
use  in  exposing   a  fresh  surface  until  that  exposed  is 
burned,  as  far  as  can  be  done  with  the  moderate  heat 
allowed  at   this  stage  of  roasting.     The  guide   is,  that 
the  ore  must  be  stirred  as  soon  as  it  is  seen  to  become 
dark  on  the  surface. 

79.  The  draft  is  regulated  so  as  to   cause   as   much 
air  to  enter  as  is  consistent  with  the  required  heat;  hence 
the  doors  on  the  working  side  are  left  open   during  all 
the  earlier  part   of  the  roasting,  though  it  may  be  nec- 
cessary  to  close  them   during  the  intervals   of  stirring, 
at  least  on  the  first  hearth,  for  the  finishing  at  a  high 
heat.     Even  the  back  doors  may  be  left  ajar  at  the  rear 
ends,  at  times,  with  great  advantage,  because  the  ma- 


or  THE 

UNIVERSITY    \ 
or  J 


44  SPECIAL    DIRECTIONS GOLD. 

terial  now  under  consideration,  being  nearly  half  sul- 
phur, requires  an  enormous  quantity  of  air,  without 
which  it  cannot  possibly  burn,  and  the  more  rapidly 
this  is  supplied  the  sooner  will  the  oxidation  be  com- 
pleted, bearing  in  mind,  of  course,  that  the  proper  de- 
gree of  heat  must  be  maintained.  At  the  same  time 
it  must  be  remembered  that  a  high  heat  at  first  is  an 
actual  disadvantage;  the  ore  roasts  faster  and  better 
with  a  low  heat,  until  oxidation  is  almost  complete. 

80.  In  thus  starting  a  furnace,  the  roasting  of  the 
charge  on  the  second  hearth  will  not  make  much  pro- 
gress until  that  on   the  first  is  so  far  advanced  that  a 
higher  heat  may  be  used,  when  it  also  will  begin  to  burn, 
and  must  be  stirred  regularly,  so  that  by  the  time  the 
first  is  finished,  probably  in  twenty  hours,  it  will  be  half 
roasted,  or  more,  and,  when  moved  to  the  first  hearth, 
will  bear  a  good  heat.     The  roasting  is  continued,  un- 
der a  gentle  heat,  as  long  as  the  sulphur  burns  actively, 
and  when  a  blue  flame,  or  a  glow,  is  no  longer  perceived 
on  stirring  the  ore,  the  heat  is  gradually  increased  until 
it  reaches  a  light   red,   approaching  yellow,   if  the   ore 
will  bear  it  without  melting  into  lumps,  as  it  will  if  it 
consists  chiefly  of  iron  or  arsenical  pyrites. 

81.  From  what  has  been  said  about  the  burning  of 
sulphur,  it  is  evident  that  the  stirring  should  be  done  at 
progressively   shorter  intervals  until   oxidation  is  com- 
pleted.    Care  must  be  taken  to  stir  quite- to  the  bottom, 
•and  in  every  corner;  and  it  is  advantageous  to  clear  the 
hearth  entirely,  a  part  at  a  time,  and  leave  it  so  for  a 
few  minutes  to  allow  of  the  oxidation  of  the  thin  strat- 
um of  ore  which  is  not  moved  by  the  hoe.     The  stirr- 
ing is  mainly  done  from  the  front  of  the  furnace,  with 


SPECIAL    DIRECTIONS GOLD.  45 

the  long  hoe;  but  occasionally  the  roaster  goes  to  the 
back,  and  with  a  small  hoe  explores  the  sides  and  cor- 
ners within  his  reach,  raking  the  ore  out,  and  pushing 
it  toward  the  middle  of  the  hearth.  In  ceasing  for  a 
time  to  stir  the  ore,  it  is  better  to  leave  the  surface 
ridged  across  by  drawing  the  corner  of  the  hoe  over  it, 
because  the  wavy  outline  thus  given  exposes  a  larger 
surface  for  oxidation,  or  for  heating.  This,  as  remarked 
by  Kustel  in  his  valuable  work  on  this  subject,  is  im- 
portant enough  to  be  attended  to. 

82.  As  the  heat,  in  this  kind  of  furnace,  is  unavoid- 
ably greater   near  the  fire   than  at  other  parts,  the  ore 
must  be  changed  from  end  to  end,  so  that  every  particle 
may,  at  one  time  or  another,  be  brought  near  to  the  fire- 
wall, or  bridge.     This  is  done  by  drawing  it  with  the  hoe 
into  a  ridge  along  the  middle  of  the  hearth,  or  better,  di- 
agonally across  it ;  then,  with  the  spade  resting  on  the 
roller  bar  as  a  fulcrum,  moving  that  ore  which  is  far- 
thest from   the  fire,  near  to  it,  placing  it  on  the   empty 
space    on    the    hearth,   and    the    reverse.     As  long  as 
sparks  can  be  seen  on  flirting  the  ore  with  the  hoe,  or 
pouring  it  off  the  spade,  the  roasting  is  not  perfect,  nor 
does  the  ceasing  of  this  appearance  prove  that  it  is  so. 

83.  The  roasting,  under  a  strong  heat,  is  continued 
until  all  the  iron  sulphate  is  decomposed,  which  may  be 
known  by  taking  a  little  of  the  ore  on  a  small  sampling 
shovel,  and  throwing  it  into   a  cup  containing  a   little 
water.      In  a  minute  the  water  will  be  clear,  and  if,  on 
adding  a  few   drops  of  solution  of  potassium  ferridcy- 
anide,  or  red  prussiate  of  potash,  a  blue  or  green  color- 
ation is  seen,  the  roasting  is  not  perfect.     After  a  little 
practice,  this  test  may  be  dispensed   with,  as  the  iron 


46  SPECIAL  DIRECTIONS GOLD. 

sulphate  is  very  easily  decomposed.  The  presence 
of  a  little  of  it  is  not  fatal  to  the  chlorination,  but 
it  causes  a  larger  consumption  of  chlorine. 

84.  Copper  sulphate,  if  present,  remains  after  iron 
sulphate  disappears,  requiring  a  long  time  and   a   high 
heat  for  its  complete  decomposition,  which,  however,  is 
not    absolutely    necessary.      It  gives,    with  the  ferrid- 
cyanide,  a   brown  or   yellow    precipitate,   which,  in  the 
presence  of  iron  sulphate  makes  a  green   coloration  by 
mixing  with  the  blue  of  the  iron. 

85.  If  it  is  desired  to  roast  to  complete  decomposi- 
tion of   copper  sulphate,  a  test  is   made  by  washing  a 
small  quantity  of  the  ore  on  a  filter,  in  a  glass  funnel, 
with  hot  water.     To  the  water  which    passes    through 
the  filter  is   added   ammonia,  and  if  even  a   very  little 
copper  is  present,  a  blue  color  is  produced.      It  will  not 
do,  in  this  test,  to   add  the  ammonia  without  removing 
the  ore  by  filtration,  because  the  blue  color  would  then 
be   produced  by  copper  oxide,  which  remains  after  the 
sulphate  is  decomposed. 

86.  When   the   roasting  is  finished,  a  careful  pan- 
ning or  horning  of  a  little   of  the   ore   will,  in  general, 
show   the    gold   plainly  ;     if  not,  then   grinding  finely 
in  a  mortar,  and  panning,  should   make    it    visible,  at 
least    with    a    lens.         But     it     happens     with    some 
ore  that  very  little  of  the  gold  can  be  seen  even  in  this 
way,  perhaps  because  of  its  extreme  fineness,  causing  it 
to  be  lost  in  the  most   careful  washing.      No  sulphides 
should  be  visible,  or  only  a  few  minute  particles  which 
the  grinding  may  have  brought  out. 

The  roasting  of  the  first  charge  being  completed,  it 
i  s  drawn  from  the  furnace  and   spread  on   the   cooling 


SPECIAL  DIRECTIONS GOLD.  47 

floor.  The  second  charge  is  moved  down  to  the  first 
hearth,  and  a  third  is  put  on  the  second  hearth.  The 
charge  now  on  the  first  hearth,  having  been  all  the  time 
roasting  on  the  second,  will,  if  it  has  been  properly  at- 
tended to,  be  almost  done,  and,  with  a  good  heat,  will 
be  finished  in  a  few  hours,  while  the  third,  having  con- 
sequently but  a  short  time  to  roast  on  the  second 
hearth,  will  take  longer  on  the  first,  when  moved  down, 
but  this  irregularity  will  gradually  disappear,  and  after  a 
few  days  the  charges,  if  equal  in  quantity  and  properly 
attended  to,  will  remain  an  equal  length  of  time,  on 
each  hearth,  and  the  discharges  will  take  place  regularly. 

87.  A  furnace  with  two  hearths,  or  even  with  three, 
does  not  allow  of  a  continuous  strong  fire.     The  heat  is 
reduced  each   time   that  a  charge  is  moved  down,  and 
not  until  a  strong  smell  of  burning  sulphur  is  no  longer 
evolved  by  the  roasting  ore,  is  the  heat  raised  gradually 
to  the  finishing  point.     The  great  fault  of  most  begin- 
ners is  in  using  too  much  heat,  especially  in  the  early 
stages  of  roasting.     A    waste    of   fuel    and  of  time  is 
caused  by  using  a  higher  heat  than  is  necessary,  for  the 
oxidation  proceeds  faster  under  a  low  heat  at  first,  and 
the  ore  assumes  a  better    condition   for    the  action  of 
chlorine,  being  more  porous,  and  lighter.      Especially  is 
this  the  case  when  lead  is  present.      Even  at  the  finish, 
too  high  a  heat  may  melt  the  gold  particles  together,  or 
to  a  spherical  form,  which  is  disadvantageous,  because 
of   exposing   a  smaller    surface   than  any  other  for  the 
chlorine  to  act   upon.     The  workman  must  use  judg- 
ment, and  acquire  experience,  before  he  can  roast  well, 
and  with  the  least  consumption  of  fuel. 

88.  The  roasting  of  concentrated  sulphides,  consist- 


48  SPECIAL  DIRECTIONS GOLD. 

ing  chiefly  of  iron  or  arsenical  pyrites,  requires  from  20 
to  30  hours,  in  a  reveberatory  furnace  with  two  or  three 
hearths. 

89.  The   roasted  and  partially  cooled  ore  is  moist- 
ened, by  spraying  with  water  from  a   hose,    the  finger 
being    placed    partly    over   the    nozzle    to    spread    the 
stream,  or  a  sprinkler  may  be  employed.     To  equalize 
the  moisture,  the  ore  is  mixed  by  means  of  a  hoe   or 
shovel.     The  degree  of  moisture  required   varies.      If 
the  gold  is  in  very  fine  particles,  the  ore  is  made    only 
so  damp  as  not  to  dust,  and  to  cohere  slightly  on  being 
compressed  in  the  hand.      If  the  gold  is  coarser,  more 
moisture  is  required,  sometimes  as  much  as  can  be  used 
without  making  the  ore  so  wet  as  to  settle  into  a  com- 
pact mass,  for  it  must  be  loose  and  porous  in  the  chlo- 
rinating vats.      The  use  of  more  water  than  is  neces- 
sary is    disadvantageous,   because  it    causes  a  greater 
consumption  of  chlorine. 

It  is  beneficial  to  allow  the  ore  to  remain  a  number 
of  hours,  even  a  day  or  two,  in  a  moist  heap  before  pro- 
ceeding further,  as  this  enables  the  moisture  to  pene- 
trate and  soften  any  lumps  which  may  have  been 
formed  in  the  roasting.  If  this  is  done,  the  surface  of 
the  heap  should  be  sprayed  from  time  to  time,  to  coun- 
teract drying,  and  before  charging  a  vat  the  ore  must 
be  re-examined,  to  insure  its  being  in  the  right  condition 
as  to  moisture.  It  is  next  to  be  placed  in  the  vat. 

90.  Charging  the  Vat.      If  the  filter  in   the    vat  is 
made  of  sand,  on  the  gravel,  and  is  wet  from  previous 
use,  it  is  advisable  to  dry  it  somewhat  by  laying  on  it  a 
few  hundred  pounds  of  dry  roasted  ore,  which  soon  be- 
comes   moist   by  drawing  the  water    out    of   the  sand, 


SPECIAL    DIRECTIONS GOLD.  49 

whence  it  will  be  seen  that,  if  the  moistened  ore  were 
put  in  it  at  once,  it  would  become  too  wet,  and,  by  pack- 
ing, would  obstruct  the  passage  of  the  chlorine,  causing 
a  back  pressure  which  would  force  the  gas  through  the 
water  joints  of  the  generator.  After  the  dry  ore  has 
been  an  hour  or  so  in  the  vat,  and  has  become  damp> 
it  is  removed,  and  the  charging  is  proceeded  with.  If 
only  gravel  and  burlap  are  used  on  the  perforated  false 
bottom,  for  a  filter,  this  precaution  is  not  needed,  and 
time  is  saved. 

91.  When  charging  a  vat  for  chlorination,  the  dis- 
charge pipe  is  stopped  with  an  oiled  plug,  and  hung  up, 
and  the  moist  ore  is   sifted  into   the   vat.     The  lumps 
which  are  retained  by  the  sieve,  are  removed  from  time 
to  time,    to    be  afterwards  recrushed,  with    rollers    or 
otherwise,  and  returned  to  the  roasting  furnace.     Any 
scraps  of  iron  which  may  have  found  their  way  into  the 
ore,  and  which  would  be  very  detrimental  to  the  chlori- 
nation, are  removed  by  the  sifting.     As  the  ore  cannot 
be  spread  evenly  over  the  filter  by  the  sifting,  and  as  it 
packs  a  little  where  it  falls,  it  is  distributed  and  loosen- 
ed with  an  iron  rake.     The  vat  is  filled  to  within  four 
inches  of  the  top,  and  the  ore  is  very  slightly  packed 
around  the  side,  by  pressing  it  with   the  hand,   so   that 
the  chlorine   cannot  make  its  way  between   it  and  the 
staves,  but  is  forced  to  permeate  the  entire  mass. 

92.  Chlorination. — Time  may  be  saved  by  starting 
the  chlorine  generator  as  soon  as  the  vat  is  about  half 
charged,  as  the  filling  will  be  completed  before  the  gas 
can  reach  the  surface. 

The  progress  of  the  chlorine   is   watched,   after   the 
charge  of  ore  is  in,  by  making  a  few  little  excavation 


50  SPECIAL    DIRECTIONS GOLD. 

and  holding  therein  a  glass  rod  clipped  in  am- 
monia, which  instantly  shows  the  presence  of  chlo- 
rine by  a  dense  white  fume.  The  moist  stopper 
of  the  ammonia  bottle  may  be  used  instead  of  a 
glass  rod.  As  soon  as  the  chlorine  has  risen  to  within 
a  few  inches  of  the  surface  of  the  ore,  the  holes  are 
lightly  filled,  and  the  cover  is  let  down  into  its  groove, 
or  rabbet,  and  luted  with  a  paste  made  of  clay  and  sand, 
in  such  proportions  as  not  to  crack  in  drying;  or  the 
luting  is  kept  moist  by  placing  wet  cloths  on  it.  The 
plug  hole  in  the  cover  is  left  open  until  the  vat  is  quite 
filled  with  chlorine,  as  shown  by  the  fume  when  ammo- 
nia is  held  to  the  hole,  which  is  then  tightly  plugged. 

If  at  this  time  the  chlorine  generator  is  not  required 
for  another  operation,  and  if  the  evolution  of  gas  has 
become  so  slow  that  it  only  bubbles  through  the  wash 
bottle  at  intervals  of  many  minutes,  it  is  well  to  leave  it 
connected  with  the  vat  ;  otherwise  it  is  disconnected, 
the  lead  nipple  in  the  vat  is  plugged,  or  the  vent  pipe 
connected,  and  the  chlorine  pipe  is  either  applied  to 
another  vat,  or  the  end  is  passed  out  of  doors.  The 
vat  is  now  left  undisturbed  for  from  12  to  40  hours,  to 
allow  the  chlorine  to  act  on  the  gold. 

When  two  or  more  vats  are  impregnated  at  one  time, 
the  forked  lead  pipe  is  used,  the  flow  of  chlorine  to  each 
vat  being  controlled  by  a  pinch-cock,  for  which  a  clothes 
pin  answers  very  well,  applied  on  the  rubber  part  of  the 
branch  pipe  ;  or  a  lead  pipe  may  be  laid  alongside  of 
the  vats,  with  a  nipple  and  lead  faucet  to  connect  with 
each  of  them  by  a  short  piece  of  rubber  tube. 

93.  Leaks  in  any  part  of  the  apparatus  are  easily  lo- 
cated by  the  aid  of  ammonia,  as  above  explained,  and 


SPECIAL    DIRECTIONS GOLD.  51 

the  operator's  nose  should  be  excused  from  this  duty, 
or  serious  consequences  may  follow.  Leaks  in  pipe- 
joints  can  usually  be  stopped  with  oil  or  lard,  and  those 
in  the  vat-cover  with  a  paste  of  oil  and  sand,  or  earth. 
The  charging-  of  a  vat  accupies  from  one  to  two  hours, 
as  the  sifting  is  very  tedious. 

94.  Making  Chlorine.  To  produce  enough  chlorine 
for  three  or  four  tons  of  roasted  ore,  the  charge  for  the 
generator  is  about: 

Manganese 30  pounds 

Salt 40 

Water . 36 

Sulphuric  acid  of  66°  Beaume 7o       " 

Or  the  same  of   salt  and   manganese, 

Water 32 

Acid  of  63°  Beaume 74       " 

The  cleaning  out  pipe  of  the  generator  being  securely 
plugged,  the  salt,  manganese,  and  water  may  be  put  in 
at  any  time,  and  stirred  with  a  wooden  paddle.  The 
acid  is  weighed  or  measured,  and  kept  at  hand  in  a 
vessel  of  lead,  or  enamelled  iron,  though  the  enamel 
generally  soon  peels  off.  The  naked  iron  does  very 
well  for  strong  acid.  The  cover  of  the  generator 
being  let  down,  the  water  joints  all  filled,  and  the  pipes 
connected,  a  fire  is  made  in  the  fire-place,  or  steam  is 
turned  into  the  heater,  to  warm  the  apparatus  some  time 
before  the  chlorine  is  wanted. 

When  all  is  ready  for  the  chlorine  to  enter  the 
vat,  a  portion  of  the  acid  is  poured  into  the 
generator  through  the  funnel,  and  mixed  by  turning  the 
stirrer.  Chlorine  soon  begins  to  pass,  and  can  be  seen 
in  the  wash  bottle  by  its  greenish  color.  It  must  pass 


52  SPECIAL    DIRECTIONS GOLD. 

in  a  lively  stream  through  the  water,  and  when  the 
current  slackens,  more  acid  is  put  in  until  the  whole  is 
used. 

From  time  to  time  the  stirrer  is  turned  carefully. 
Sometimes  it  must  be  lifted  a  couple  of  inches  before 
the  impacted  stuff  can  be  loosened,  and  this  is  the 
reason  why  the  water  joint  in  this  part  is  made  two 
inches  deeper  than  in  the  others  ;  otherwise  the  lifting 
of  the  stirrer  might  cause  an  escape  of  gas  which 
would  be  injurious,  and  might  be  dangerous,  to  the 
workman.  During  the  operation  the  apparatus  is 
gradually  heated,  but  not  so  as  to  make  the  contents 
boil. 

By  the  time  the  charge  is  exhausted  the  test  by 
means  of  ammonia  should  indicate  an  abundance  of 
chlorine  issuing  from  the  holes  in  the  vat  covers.  If 
this  is  not  the  case,  more  manganese  and  salt  must 
be  put  into  the  generator,  through  the  opening  pro- 
vided for  that  purpose,  but,  as  the  workman  is  liable  to 
suffer  serious  inconvenience  from  the  escaping  gas 
while  doing  this,  it  is  better  to  avoid  the  necessity  by 
putting  in  enough  at  first.  If  an  additional  quantity  of 
the  other  materials  is  used,  more  acid  will  also  be  re- 
quired, unless  an  excess  was  taken  for  the  charge,  but 
this  can  be  introduced  without  inconvenience  by  means 
of  the  pipe  and  funnel.  The  relative  proportions  of  the 
materials  vary  according  to  their  purity,  and  the  quan- 
tity of  chlorine  required  depends  much  on  the  character, 
and  more  or  less  perfect  roasting,  of  the  ore  ;  hence  no 
fixed  rule  can  be  given  for  either. 

95.  When  it  is  desired  to  prepare  the  generator  for 
another  operation,  the  end  of  the  rubber  tnbe  leading 


SPECIAL  DIRECTIONS GOLD.  53 

from  the  wash  bottle  is  passed  out  of  doors,  or  con- 
nected with  a  charged  vat.  Water  is  poured  into  the 
water  chamber,  b,  and  passes  to  the  interior  of  the 
generator  through  notches  cut  in  the  lower  edge  of 
the  cover  for  that  purpose,  and  fills  it,  expelling  all 
gaseous  chlorine,  which  would  otherwise  escape  into 
the  room  on  raising  the  cover,  or  removing  the  plug  at 
d.  The  water  is  allowed  to  stand  for  some  time  in  the 
generator,  to  dissolve  the  sodium  sulphate  formed  by 
the  action  of  sulphuric  acid  on  salt,  which  sometimes 
forms  a  hard  incrustation,  if  too  much  heat  has  been 
applied.  The  plug  at  d  is  then  withdrawn,  and  the 
generator  is  emptied  through  the  pipe,  which  should 
deliver  out  of  the  room. 

If  there  is  any  impacted  residue  which  cannot  be  re- 
moved by  a  stream  of  water  from  a  hose,  directed 
through  one  of  the  openings,  the  main  cover  is  raised 
and  the  stuff  carefully  scraped  off  the  bottom,  but  if 
not,  the  recharging  can  be  done  by  the  opening,  k,  with- 
out raising  the  cover.  If  the  residue  contains  much 
unchanged  salt,  the  proportion  used  should  be  reduced. 
An  excess  of  manganese  shows  itself  by  its  blackness. 
When  the  ingredients  have  been  correctly  proportioned, 
only  a  dark  grey  sediment  remains  with  the  more  or 
less  acid  liquid. 

96.  Leaching  the  Gold  Ore. — After  the  ore  is  sup- 
posed to  have  remained  long  enough  in  contact  with 
chlorine — that  is,  from  12  to  40  hours — the  plug  hole 
in  the  cover  is  opened,  and  tried  with  ammonia  as  be- 
fore. This  must  still  produce  a  dense  fume  ;  if  not,  the 
chances  are  that  a  poor  result  will  be  obtained  in  leach- 
ing, unless  chlorination  is  repeated.  If  appearances 


54  SPECIAL    DIRECTIONS GOLD. 

are  satisfactory,  a  little  ore  is  taken  out  through  the 
hole  with  a  sampler,  finely  ground,  and  carefully  washed 
in  a  saucer,  or  a  horn.  Neither  gold  nor  sulphides 
should  be  visible  with  a  lens,  but,  as  before  remarked, 
some  ores  do  not  show  the  gold  well,  even  before  chlo- 
rination,  and  for  such  this  test  is  not  conclusive. 

97.  At  this  point  a  difficulty  arises,  from  the  fact 
that  a  large  quantity  of  chlorine  remains  in  the  vat,  the 
escape  of  which  into  the  leaching  room  is  not  desirable. 
If  the  cover  of  the  vat  be  raised,  the  gas  is  visible  like 
a  green  sea  above  the  ore  ;  a  pestilential  sea  whose 
waves,  surging  forth  upon  the  slightest  disturbance  of 
the  air,  threaten  to  envelope  and  suffocate  the  work- 
man, unless  he  hold  his  breath  while  hoisting  the  cover 
and  fastening  the  tackle,  and  then  retreat  in  haste  till 
the  storm  is  over ;  and  even  then  the  same  trouble  re- 
curs while  water  enters,  and  displaces  the  chlorine  still 
remaining  beneath  the  filter,  and  permeating  the  loose 
mass  of  damp  ore. 

To  overcome  this  difficulty,  some  operators  fill  the 
vat  with  water  before  lifting  the  cover,  and,  by  means 
of  a  rubber  hose,  convey  the  expelled  gas,  either  out  of 
doors,  or  into  another  vat  charged  with  ore.  There 
are  two  objections  to  this  plan — firstly,  a  great  deal  of 
chlorine  is  absorbed  by  the  water,  which  has  an  un- 
favorable effect  in  the  precipitation  of  gold,  making  it 
more  difficult  to  settle,  as  well  as  wasting  the  precipi- 
tant ;  and,  secondly,  the  water,  entering  the  tub  in  one 
large  stream,  descends  through  the  bed  of  ore  at  one 
point,  and  rises  through  it  in  other  parts,  giving  a  solu- 
tion of  nearly  uniform  strength  throughout  the  mass, 
and  requiring  a  large  quantity  of  water  to  complete  the 


SPECIAL  DIRECTIONS — GOLD  55 

leaching,  taking  more  time,  and  giving  finally  a  weaker 
solution  than  is  necessary,  for  the  precipitation  takes 
place  better  when  the  solution  is  strong. 

The  best  way  to  apply  the  water  is  by  spraying  it  all 
over  the  surface  of  the  ore  in  the  vat,  so  that,  percolat- 
ing downward  through  the  mass,  it  carries  the  greater 
part  of  the  gold  chloride  in  the  first  portion  of  the 
water,  and  a  rich  solution  is  obtained  at  once,  while 
less  water  is  required  to  remove  the  whole  of  the  gold, 
and  the  stronger  solution  thus  finally  obtained  gives  a 
better  precipitation  on  addition  of  iron  sulphate.  But 
if  the  spraying  is  undertaken  by  hand  with  a  sprinkler* 
the  loose  ore,  settling  as  it  becomes  wet,  expels  chlorine 
in  such  volumes  as  to  render  it  impossible  for  a  man  to 
stand  near  the  vat. 

The  course  I  adopted  was  to  place  a  coil  of  lead  or 
rubber  pipe,  in  which  were  numerous  small  holes,  around 
the  vat  under  the  cover.  After  raising  the  cover,  the 
water  supply  pipe  was  connected  with  the  perforated 
coil,  and  the  water,  under  moderate  pressure,  issued  in 
a  number  of  fine  jets,  and  showered  all  over  the  ore, 
through  which  it  descended  gradually,  dissolving  the 
gold  chloride  as  it  passed,  so  that  the  first  solution  which 
passed  through  the  filter,  and  filled  the  space  under  it, 
was  very  rich,  while  that  which  finally  remained  on  the 
top  was  very  weak.  The  discharge  was  then  started, 
and  the  water  thenceforth  admitted  in  the  usual  way, 
keeping  the  surface  of  the  ore  covered  until  the  leach- 
ing was  finished.  This  plan,  however,  is  still  open  to 
the  objection  that  it  gives  a  solution  containing  much 
free  chlorine,  while  the  chlorine  which  is  expelled  is 
not  removed  from  the  room ;  hence  it  is  very  desirable 


56  SPECIAL    DIRECTIONS— GOLD. 

that  means  should  be  used  to  abstract  the  surplus  from 
the  vat  before  raising  the  cover,  or  admitting  water. 
The  appliance  I  am  about  to  describe  will  not  only  do 
this,  but  will  also  save  the  chlorine,  for  use  in  another 
charge  of  ore,  with  little  waste. 

98.  Before  lifting  the  cover,  the  plug-hole  being 
open,  one  of  the  lower  openings,  either  the  nipple 
through  which  the  gas  was  admitted,  or  the  discharging 
pipe,  is  connected  by  a  rubber  hose  with  the  interior  of 
an  inverted  bell  of  sufficient  size,  which  is  immersed  in 
a  tank  of  water,  precisely  like  the  "gasometer"  of  gas- 
works, and  like  it,  counterpoised  and  suspended  by 
ropes  or  chains  passing  over  rollers,  so  as  to  allow  the 
bell  to  rise  or  fall  in  its  water  tank.  By  adding 
weights  to  the  counterpoise,  the  bell  is  gradually  raised, 
and  the  chlorine  is  withdrawn  from  the  vat  and  enters 
the  bell,  while  air,  entering  the  vat  through  the  open 
plug-hole  in  the  cover,  replaces  the  abstracted  chlorine. 
The  filling  of  the  vat  with  water  is  then  proceeded  with 
in  any  way  that  may  be  convenient,  without  annoyance 
from  escaping  chlorine.  The  chlorine  in  the  bell  may 
be  again  expelled  when  wanted,  and  caused  to  enter  the 
same,  or  another  vat,  by  simply  removing  a  part  of  the 
counterpoise,  and  allowing  the  bell  to  descend  by  its 
own  weight. 

When  the  ore  in  the  vat  is  covered  by  the  water,  the 
discharge  pipe  is  let  down  to  the  trough  which  leads  to 
the  gold  tub,  and  the  plug  is  removed  from  it.  To  pre- 
vent disturbance  of  the  ore  by  the  water  flowing  into 
the  vat,  the  stream  is  received  on  a  perforated  board, 
or  on  a  sack  laid  upon  the  ore.  The  inflow  and  the 
outflow  must  be  equal,  so  that  the  ore  remains  sub- 


SPECIAL    DIRECTIONS GOLD.  57 

merged.  If  the  outflow  is  too  rapid,  it  is  lessened  by 
simply  "  kinking  "  the  pipe,  which,  for  this  reason,  is  of 
pure  rubber,  and  long  enough  not  only  to  reach  the 
trough,  but  a  foot  or  so  more  ;  it  can  then  be  "  kinked  " 
so  as  to  entirely  stop  the  flow  if  desired. 

99.  A   few  ounces  of  the    strong  solution    of  gold 
chloride  first  obtained,  are  set  aside  for  a  purpose  which 
will  shortly   appear.      If   the   ore    contains  no  copper, 
and  has  been   properly    roasted,  the  lixivium  will  be  of 
an  amber  color.     A  green  hue   indicates  the  presence 
of   copper,  and  a  very  dark,  almost  black,  appearance, 
produced  by  iron  perchloride,  shows  that  the  ore  has 
been  improperly  roasted. 

100.  Precipitating  the    Gold.  —  On    beginning   the 
leaching,  about  a  dozen  gallons  of  the  solution  of  iron 
sulphate  is  let  into   the    gold    tub   (for    exceptions    see 
article  on  precipitating  gold,  under  "  Addenda.")     The 
gold   is    precipitated    as  a   brown  powder,  which,  how- 
ever, requires    many    hours    to    settle.     The  object  of 
putting  the  precipitant  into  the  gold  tub  in  advance,  is 
to  decompose    the    gold   solution,   and  precipitate    the 
gold,  as  soon  as  it  enters  the  tub,  so  as  to  lessen  the  loss 
by  absorption  into  the  wood,  by   an  accidental  leak,  or 
an   overflow  ;    also   to   neutralize  the  free   chlorine   in 
the  lixivium. 

101.  When  the  solution  flowing  from  the   leaching 
vat  has   become   colorless,  or  before,  if  much  copper  is 
present,  a  little  of   it  is    received   from   the   hose    in   a 
glass  vessel,  such  as    a  beaker,  tumbler,  or  ore  sample 
bottle,  and  some  solution  of  iron  sulphate  is  added.      If 
gold  is  present,  a  dark  cloud  is  produced,  either  instant- 
ly or  after  the  lapse  of  a  few  seconds.     When   only  a 


58  SPECIAL  DIRECTIONS GOLD. 

slight  discoloration  is  produced  in  the  lixivium,  by  the 
addition  of  iron  sulphate,  it  is  better  to  divert  the 
stream  into  one  of  the  extra  gold  tubs,  or  "  gold  wash- 
tubs,"  because  the  metal  obtained  from  very  weak  lixiv- 
ium is  so  extremely  fine  as  to  settle  with  difficulty,  and 
even  to  pass  through  a  filter.  The  leaching  is  contin- 
ued until  not  a  trace  of  gold  can  be  detected  in  the 
lixivium  coming  from  the  vat. 

102.  I  will    here   call   attention   to   a  circumstance 
which  was  observed  in    my    works.     After    the    leach 
ceased   to  show  gold    by  the  iron  sulphate  test,  if  the 
discharge  was  stopped    for   a    few   minutes,    and   again 
started,  the  solution  would  again    give  a  considerable 
precipitation   on    being  tested,  but   in    a   few    minutes 
would  again  fail  to  show  even  a  trace,  and  this  could  be 
repeated  several  times.      It  was  due  to  unequal  percola- 
tion, and   is  mentioned    here   in  case   the  same  might 
occur  in  other  works. 

103.  The   solution   in  the  gold   tub   is  well  stirred 
with  a  wooden  paddle,  and,  after  waiting  for  a  few  min- 
utes, to  allow  the  gold  to  settle  a  little,  a  sample  is  taken 
in  the  glass,  and  tested  by  adding  some  iron   sulphate. 
If  any  discoloration  is  produced,  more  iron  sulphate  is 
needed  in  the  tub.     If  none,  yet,  as  an  excess  does  no 
harm,  it  is  best  to  make  sure  that  there  is  enough  of  the 
precipitant,  by  emptying  the  glass,   rinsing  it  once  or 
twice  with  the  liquid  from  the  gold  tub,  taking  another 
sample,   and  testing  it  by  adding  some   of  the  strong 
solution  of  gold,   which,   it   will    be   remembered,  was 
set  aside  at  the  beginning  of  the  leaching.      If  a  dark 
cloud    is  now    produced,   it  is  certain  that  enough  of 
the  iron  sulphate  has  been  used  in  the  gold  tub.      If 


SPECIAL    DIRECTIONS GOLD.  59 

not,  it  is  safest  to  add  another  bucketful,  mix  thor- 
oughly, and  try  again.  By  taking  the  trouble  to  make 
this  check  test,  an  expensive  accident  may  be  avoided. 

104.  The   gold  settles  better  if  the  stirring  is  re- 
peated after  an  hour  or  two,  and  it  is  advantageous  to 
add  a  few  pounds  of  sulphuric  acid.      If,   in  stirring,  a 
.circular  motion  is  imparted  to  the  liquid,  nearly  all  the 
gold  will  settle  near  the  middle  of  the  tub.     The  gold 
requires  from  24  to  48  hours'to  settle. 

105.  The  weak  leach  in  the  wash-tub  may  be  treated 
with  some  of  the  iron  sulphate,  to  throw  down  the  small 
quantity  of  gold  which  it  contains,  which  must  then  be 
allowed  abundant  time  for  settling;  or*it  may  be  raised 
by  means  of  a  wooden  or  leaden   pump,  and    used  to 
begin  the  leaching  of  the  next  charge  of  ore.     A  third 
way,  which  suggests  itself,  but  has  not  been  tried,  ex- 
cept, as  will  be  seen  hereafter,  in  connection  with  the 
extraction  of  silver,  is  to  precipitate  the  gold,  together 
with  any  remains  of  copper,  etc.,  which  may  be  present^ 
by  an  addition  of  calcium  polysulphide,  the  preparation 
of  which  will  be  described  in  its  place.    A  great  excess 
of  the  precipitant  should  be  avoided,  because  the  gold 
tersulphide  which  it  produces   is   somewhat  soluble  in 
calcium  polysulphide.     The  precipitate  obtained  in  this 
way  would  probably  settle  more  rapidly  than  the  other. 

106.  Iron  S^dphate  Solution.     This  precipitant  for 
gold  may  be  prepared  by  dissolving  common  copperas, 
or  green  vitriol,  in  water.     A  quantity  of  the  crystals  is 
placed  in  the  vat  prepared  for  it,  which,  it  will  be  remem- 
bered, contains  a  filter,  and  water  is  added.   There  should 
always  be  an  excess  of  copperas  on  the  filter,  in  order 
that  the  solution  may  be   saturated.      It  may  also  be 


60  SPECIAL    DIRECTIONS — GOLD. 

prepared  by  dissolving  scrap  iron  in  diluted  sulphuric 
acid.  Several  days  must  be  allowed  for  the  preparation 
of  the  solution  by  this  method,  and  an  excess  of  iron 
must  always  be  present  in  the  dissolving  tub,  the  sup- 
ply of  solution  being  maintained  by  the  addition  of 
dilute  acid  from  day  to  day,  and  of  iron  as  fast  as  it 
disappears. 

107.  When  the  liquid  in  the  gold  tub   has  become 
perfectly    clear,   the    discharge    pipe    is  freed,  with  its 
float,    and    the '  liquid    is    allowed    to    flow  through    a 
filter  of   sand    or    sawdust,     because  some    fine    gold 
always    remains    in    suspension,    even    after    48  hours' 
settling.      If  a  sand  filter  is  used,   it  is,   after  a  time, 
taken   up    and  chlorinated,  like   ore.    If   if  is  of  saw- 
dust, it  is  thrown  into  the  furnace  with  ore,  and  burned, 
or  burned  by  itself  and  the  ashes  collected. 

If  the  discharge  pipe  of  the  gold  tub  does  not  sink 
deeply  enough  to  draw,  a  piece  of  board  is  laid  over  it, 
which  keeps  it  below  the  surface,  and  follows  it  down. 
If  it  tends  to  draw  too  deeply,  by  being  sucked  down,  a 
larger  float  should  be  used;  or  a  cord  attached  to  the 
float,  and  turned  around  a  nail  in  the  side  of  the  tub, 
will  secure  it ;  but  it  is  then  necessary  to  slacken  the 
cord  from  time  to  time.  If  the  hose  is  rather  stiff,  and 
well  adjusted,  it  will  give  no  trouble.  The  construction 
of  the  float,  encircling  the  end  of  the  hose  with  a  thick- 
ness of  two  inches  of  wood,  obviates  all  danger  of  a  loss 
of  the  precipitated  gold  by  drawing  too  near  the  bot- 
tom of  the  vat.  Other  arrangements  for  drawing  off 
the  liquid  will  be  found  under  "  Addenda." 

108.  Collecting  the    Gold. — Unless   when    working 
very  rich  ore,  or  for  special  reasons,  the  gold  is  not  re- 


SPECIAL    DIRECTIONS GOLD.  61 

moved  from  the  tub  until  several  precipitations  have 
been  made.  When  a  clean-up  is  desired,  the  liquid  is 
drawn  off  as  closely  as  may  be  done  without  loss  of  gold 
as  described  ;  the  remainder,  with  some  of  the  gold,  is 
allowed  to  flow  through  the  faucet  into  a  small  tub. 
The  greater  part  of  the  gold  remains  on  the  bottom  of 
the  precipitating  tub,  and  is  taken  up  with  a  scoop,  and 
carried  in  a  suitable  vessel,  such  as  an  enamelled 
kettle,  to  the  filters.  The  bottom  of  the  gold  tub  is 
washed  by  means  of  a  small  stream  of  water  from  a 
hose,  and  a  whisk  broom.  The  washings  are  added  to 
the  drainings  in  the  small  tub,  and  are  either  allowed  to 
settle  again,  and  again  drawn  off,  or  taken  at  once  to 
the  filters. 

109.  Washing  the  Gold.—  When  drained  in  the  fil- 
ters, the  gold,  if  nearly  clean,  which  is  known  by  its 
having  a  brown  color,  not  too  dark,  may  be  washed  at 
once  on  the  filter,  with  hot  dilute  sulphuric  acid  and 
salt,  or  dilute  hydrochloric  acid,  and  afterwards  with 
hot  water  alone ;  if  very  impure,  it  is  transferred 
to  a  large  porcelain  dish,  and  boiled  on  a  sand  bath 
with  slightly  diluted  acid.  After  adding  water,  it  is 
again  thrown  on  the  filter,  drained,  and  washed  with  hot 
water  until  the  latter  comes  through  tasteless.  The 
filter  bags,  to  which  some  gold  adheres,  are  kept  under 
water  in  a  suitable  vessel,  to  prevent  rotting,  until 
wanted  again.  When  worn  out,  they  are  lightly 
sprinkled  with  powdered  nitre,  dried  in  an  iron  dish, 
and  touched  with  a  live  coal.  They  then  burn  like 
touchpaper,  and  the  ashes  are  added  to  the  precipitated 
gold.  Too  much  nitre  must  not  be  put  on  the  bags, 


62  SPECIAL    DIRECTIONS GOLD. 

or  the  combustion  will  be  too  violent,  and  gold  may 
be  lost. 

110.  Drying  the  Gold. — The  washed  gold  is  pressed 
by  hand   in  the  filter  bags,  transferred  to  an  iron  dish, 
and  almost,  but   not  completely,  dried.     While    drying 
it  is  mixed  with  a  little   powdered  borax  and  nitre.      If 
several  ounces  of  nitre  are  used,  on  account  of  impuri- 
ties in  the  gold,  it  is  advisable  to  add  about  half  as  much 
clean    quartz    sand,  to  protect   the  crucible    from    the 
action  of  the  nitre  during  the  subsequent  melting  of  the 
metal.      The  purpose  of  allowing  the  pulverulent  metal 
to  retain  a  little  moisture  is,   the  prevention  of  loss  by 
dusting  while  putting  it  into  the  melting  pot. 

111.  Melting  the   Gold. — If  the  gold  is  very  clean, 
it  may  be  melted  in  a  black  lead  pot,  but  I  have  always 
preferred  a   sand   pot,  on   account  of  the   tendency  of 
plumbago  to  cause  contamination  of  the  gold  by  reduc- 
tion of  the  base  metal  compounds  which  may  be  pres- 
ent.    There  is,  however,  some  slight  risk  of  the  sand 
pot  breaking,  nothwithstanding  the  precaution  of  adding 
sand  with  the  nitre,  and  well  drying  the  pot  before  put- 
ting it  into  a  moderate  fire.     To    guard  against  being 
obliged  to  wash  the  gold  out  of  the   ashes  in  case  of 
breakage,  with  some  risk  of  loss  if   the  bottom  of  the 
ash-pit  is   rough,  a  black  lead  dish,  made  of  the  lower 
part  of  a  crucible,  is  placed  under  the  sand  pot. 

112.  The  fuel  used  for  melting  is  charcoal  or  coke. 
English  coke  is  so  much  better  than  that  from  the  gas 
works  as  to  compensate  for  the  extra  cost.     A  common 
portable  assay  furnace  is  very   suitable  for  the  melting 
of   moderate   quantities   of   gold,  and  a  sand  pot  about 
ten   inches  high   is  large  enough   for  several  thousand 


. 

SPECIAL    DIRECTIONS- -GOLD.  63 

dollars  worth,  although  a  larger  crucible  is  needed  than 
for  metal  which  is  in  a  more  compact  form. 

113.  When  the  crucible  is  red  hot,  it  is  taken  from 
the   furnace  and  gently  tapped,  to  ascertain  that  it  is 
sound,  then  filled  with  the  gold,  by  means  of  a  scoop, 
replaced  in  the  furnace,  covered,  and  gradually  brought 
to  a  strong  red  heat.     As  the  partly  melted  gold  settles* 
the  pot   is    refilled,  without   removal  from  the  furnace, 
by  means  of  the  scoop,    and,  if  required,  a  sheet  iron 
funnel.      It  is  important  to  refill  the  pot  before  the  con- 
tents are  quite  fused,  and  while  they  are  in  a  pasty  condi- 
tion; otherwise  some  of  the  gold  may  be  thrown  out  of  the 
crucible.     The   handling  and   melting  of  the  gold  are 
greatly  facilitated   if  the   precipitated  metal  is   pressed 
into  cakes,  and  heated  to  redness  in  a  muffle,  as  is  done 
in  the  mint  with  the  finely  divided  gold  from  the  refin- 
ing.    When    the   entire   charge   is  in,  a  white   heat  is 
maintained    until   the    gold     and    slag   are  thoroughly 
melted.     An  addition  of  more    borax  may  be  required 
if  the  slag  is  not  sufficiently  fluid.     The  mass  is  stirred 
with  a  red-hot  iron  rod,  which  must  not   be  kept  in  too 
long,  or  it  will  make  the  gold  base.     Some  metallurgists 
use  a  strip  of  black  lead  for  the  purpose. 

114.  When  the  slag  is  quite  liquid,  it  is  skimmed  off 
the  melted  gold,  by  means  of  a  piece  of  nail  rod,  which  is 
turned  at  one  end  to  a  flat  spiral,  and  bent  to  a  suitable 
angle  for  convenient  use.     This  is  dipped,  cold,  into  the 
melted  slag,  quickly  withdrawn,  and  pressed  upon  a  cold 
block  of  greased  iron,  so  as  to  flatten  the  adhering  slag, 
then  just  dipped  into  cold  water,  and  again  into  the  slag, 
repeating  the  routine  until  the  latter  is  all  removed,  and 
the  melted  gold  is  seen  in  the  pot. 


64  SPECIAL    DIRECTIONS GOLD. 

115.  It    sometimes  happens    that    the    precipitated 
gold  is  contaminated   by   lead  sulphate,  which  cannot 
readily    be    removed    in     the     washing,    and    which* 
does    not    mix    with    the   slag  proper.        This    cannot 
be  skimmed  off  in   the    manner  described,    but  is  re- 
moved by  means  of  a  red-hot  scorifier  held  in  the  tongs. 

116.  If  the  melted  metal  is  pure,  it  appears  greenish 
and  motionless,  but  if  any  base  metal  remains,  colored 
rings,  or  spots,  are  seen,  moving  from  the  center  out- 
wards.    These  rings  are  base  metal  oxides,  and  if  they 
are   supposed    to   be    caused    by  iron,  or  copper,  a  few 
pieces    of  borax  are  thrown  in,   and   allowed  to   melt 
while  the    pot  is  left  uncovered.     After  a  time  the  new 
slag  thus  formed  is  skimmed  off,  and  more  borax  put  in, 
and,   if   the  metal  is  very  impure,  a  little  nitre  is  added 
to  help  the  oxidation  of  the  base  metal,  for  if  the  opera- 
tion takes  too  long  a  time,  the    pot   will    be  cut  imme- 
diately above  the  gold.     If  the  impurity  consists  of  lead, 
a  little  bone  ash   is   better  than   borax  to   absorb   the 
oxide,  as  it  is  formed,  especially  when  a  black   lead  pot 
is  used. 

117.  When   all  is  ready,  the    pot  is  seized   by  the 
tongs  and    the   metal   is    poured  into  a  cast-iron  ingot 
mould,  which  has  previously  been  warmed  and  smoked, 
or  oiled.     A  little  oil  is  poured  on  the    top   of  the  bar 
before  it  solidifies.      Unless  the  gold  is  to  be  assayed 
and  stamped  at  the  works,  it  is  not  necessary  to  be  care- 
ful about  the   shape   or  appearance    of  the    bar.     It  is 
then  as  well,  and  saves  some  trouble,  to  allow  the  metal 
to  cool  in  the  pot,  which   is  then  broken;    in   any  case 
it   can   be  used  but   once.      But  this    cannot    be  done 
if  a  black  lead  pot  is  used,  because  it  will  serve   many 


SPECIAL    DIRECTIONS GOLD    AND    SILVER.  65 

times.  The  slag  and  pots  are  preserved,  and  either 
sold,  or  crushed  and  treated  with  quicksilver  for  the 
gold  which  they  contain. 

118.  B.   Concentrated  Pyrites  Containing  Gold  and 
Silver. — This  material  is  obtained  in  the  same  manner 
as  the  concentrations  containing  gold  only.     The  silver 
is  usually  of  secondary  importance  as  to  its  value. 

119.  Roasting. — This    is  conducted    in    the   same 
manner  as  that  for  gold,  but  as  the  chlorination  of  the 
silver  in  the  vats,  by  means  of  cold  chlorine,  does  not 
give  satisfactory  results,  it    is   better  to  form  the  silver 
chloride  in  the  furnace,  for  which  purpose  an  addition  of 
salt  is  necessary.     One  per  cent.,  or  20  pounds  to  the 
ton  of  ore,  is  generally  enough  for  fifty  ounces  of  silver. 
In   some  cases  the  salt  is  mixed   with  the  ore  when 
charged,  but  this  is  not  always  safe,  as  a  very  large  loss 
of  gold  sometimes  results. 

120.  If  it  is  found,  by  means  of  assays,  that  a  loss 
results  from  charging  the  salt  with  the  ore,  the  course 
adopted  is,  to  roast  as  directed  for  gold,  then  to  let  the 
ore    cool    somewhat     in    the    furnace,    and    throw    in 
the  salt  through    one    of    the  doors,  scattering  it   as 
much  as  possible  over  the  ore.     The  doors  are  then 
closed  until  the  salt  ceases  to  crackle,  after  which  it  is 
rapidly  and  vigorously  mixed  with  the  ore  by  means  of 
the  hoe,  and  the  charge  is  drawn  out  within  20  minutes 
after  putting  in  the  salt.    The  heat  must  be  high  enough 
to  cause  the  reaction  between  salt  the  and  the  metal 
sulphates,  yet  not  so  high  as  to  produce  heavy  fumes, 
or  blue  flames  ;   nor  should  a  yellow  substance  be  seen 
on  the  side  of  the  furnace,  where  the  ore  is  drawn  out. 
The  hot  ore  evolves  copious  fumes  of  volatile  chlorides 


66  SPECIAL    DIRECTIONS GOLD    AND    SILVER. 

and  free  chlorine.  It  is  not  spread  at  once,  but  is  left 
in  the  heap  to  be  acted  upon  by  the  gases  for  an  hour, 
after  which  it  is  spread  on  the  cooling  floor. 

121.  The   best    results  are  produced  by  adding  to 
the  ore,  before  roasting,  a  little  more  salt  than  the  quan- 
tity required  by  theory  to  chloridise  the  silver  present ; 
that  is,  for  fifty  ounces  of  silver  not  more  than  two  or 
three    pounds  of  salt,  which   should  be   finely  ground. 
The   one    per  cent,  should  be  added  at  the  finish  as 
above.     The  use  of  a  little  salt  at  the  beginning  in  this 
way  caused  no  blue  flames  of  copper  chlorides,  heavy 
fumes,  nor  loss  of  gold,  while  it  caused  an  increase  in 
the  yield  of  silver  amounting  to  three  or  four  ounces  to 
the  ton.     It  was  not  proved  whether  the  result  would 
have  been  the  same  if  the  final  addition  of  one  per  cent 
of  salt  had  been  omitted,  as  it  could  do  no  harm,  and 
cost  almost  nothing.     But  when  no  salt  whatever  was 
used,  the    result   was    unsatisfactory,  and  considerably 
more  chlorine  was  required  in  the  vats. 

Ores  differ  much  in  their  behavior  in  working,  and 
without  the  cause  of  the  difference  being  manifest,  even 
from  an  analysis.  Thus  there  are  cases  in  which  ten 
per  cent  of  salt  has  been  mixed  with  the  ore  before 
roasting,  without  causing  a  loss  of  gold.  It  therefore 
behooves  the  operator  not  to  rely  solely  on  the  instruc- 
tions given  in  any  book,  but  to  watch  his  results  carefully 
and  constantly,  until  he  has  established  a  satisfactory 
mode  of  procedure. 

122.  After  roasting,  the  work  is  carried  on  precisely 
as  directed  for  ore  containing  no  silver,  up  to  the  point 
at  which  the  gold  leaching  is  finished,  except  that  it  is 
not  necessary  to  extract  the  last  trace  of  soluble  gold 


67  SPECIAL    DIRECTIONS GOLD    AND    SILVER. 

* 

with  water,  because,  if  a  little  remains,  it  will  be  ob- 
tained with  the  silver.  It  is,  however,  proper  to  re- 
mark that,  if  the  ore  is  of  such  a  character  that  much 
salt  must  not  be  used  at  the  commencement  of  the 
roasting,  the  lumps  from  the  sifting  should  be  washed, 
to  remove  soluble  chlorides,  before  being  re-roasted. 

123.  Leaching  the  Silver. — At  this  point  some  oper- 
ators remove  the  ore  to  other  leaching  vats,  from  an 
idea  that  the  small  quantity  of  the  leaching  liquid  used 
for  silver  which  remains  in  the  filter,  is  injurious  to  the 
chlorination  of  the  next  lot  of  ore.  I  do  not  think  it 
worth  while  to  take  this  trouble.  I  even  found  it  un- 
necessary to  take  any  special  pains  to  wash  the  filters 
before  recharging,  any  further  than  is  done  in  washing 
the  hypo  out  of  the  ore,  which  is  necessary  in  order  to 
avoid  waste.  The  traces  of  hypo  remaining,  if  not  oxi- 
dized to  harmless  sulphate  by  the  action  of  air,  must  be 
so,  instantly,  on  the  admission  of  the  chlorine.  It  is 
true  that  in  the  latter  case  hydrochloric  acid  would  be 
formed,  but  in  such  minute  quantity  as  to  be  of  no  im- 
portance. At  the  worst  the  only  inconvenience  would 
be  a  slightly  increased  consumption  of  chlorine. 

When  the  gold  leaching  has  been  carried  as  far 
as  is  desired,  the  water  in  the  vat  is  allowed  to  subside 
below  the  surface  of  the  ore.  The  solution  of  calcium 
hyposulphite  is  then  admitted,  and  the  discharge  is 
directed  into  one  of  the  extra  silver  or  wash  tubs. 

It  is  best  to  have  a  separate  trough  to  convey  the 
silver  solution  to  the  tubs,  not  only  because  it  is  con- 
venient to  have  the  gold  and  silver  tubs  at  opposite 
ends  of  the  set  of  leaching  vats,  but  also  because  it  is 
often  necessary,  when  working  several  vats,  to  run  both 


68  SPECIAL   DIRECTIONS GOLD    AND    SILVER. 

gold  and  silver  solution  at  the  same  time.  I  therefore 
have  two  troughs,  extending  in  front  of  and  below  the 
leaching  vats,  side  by  side,  but  inclined  in  opposite 
directions,  so  as  to  lead,  the  one  to  the  gold,  the  other  to 
the  silver  tubs. 

The  hypo  should  never  be  allowed  to  flow  into  the 
gold  tubs,  because  it  forms  a  combination  from  which 
the  gold  cannot  be  precipitated  by  iron  sulphate.  As, 
however,  the  precipitant  used  for  silver  throws  down 
gold  also,  whether  dissolved  in  water  or  in  hypo,  there 
is  not  the  least  danger  of  losing  any  gold  which  may 
find  its  way  to  the  silver  tubs. 

124.  As  the  water  runs  out  of  the  ore  mass  in  the 
vat,   the  hypo  follows  it,  and  as  soon  as  a  sweet  taste, 
indicating   the  presence  of   silver,    is  perceptible,   the 
stream    is   turned  into  the    main    silver   tub,    because 
the    wash   water,    after    precipitation    of  any    metal    it 
may  contain,  is  thrown  away,  but  the  hypo  is  preserved 
for  future  use.    The  flow  is  not  allowed  to  be  too  rapid, 
but  is  checked  by  "kinking"  the  pipe,  as  directed  in  the 
gold  leaching.    There  is  no  guide  for  this  but  experience, 
and  the  strength  of  the  silver  solution  coming  from  the 
ore,  which  is  known  by  its  more  or  less  sweet  taste. 

125.  When  a  sweet  taste  is  no  longer  perceived  in 
the  solution  coming  from  the  vat,  a  test  is  made  by 
taking  some  of  it  in  a  glass,  and  adding  some  solution 
of  calcium  sulphide.     If  a  precipitate  is  produced,  it  is 
certain  that  metal  of  some  sort  is  still  being  extracted 
from  the  ore.     The  question  then    is,  what  metal,  or 
rather  whether  there  is  any,  or  much,  silver,  for  it  is 
an  unfortunate  circumstance  that    the    hypo  dissolves 
lead    sulphate,    and  other    base  metal  compounds,  es- 


SPECIAL    DIRECTIONS GOLD  AND    SILVER.  69 

pecially  after  the  extraction  of  silver  is  finished,  or  when 
the  hypo  is  too  strong. 

Some  idea  of  the  nature  of  the  metal  which  is 
being  extracted  by  the  hypo,  may  be  obtained  from 
the  color  of  the  precipitate.  Silver  gives  a  dark  brown, 
copper  a  reddish  brown,  lead  and  antimony  light, 
sometimes  yellowish  shades.  It  is,  however,  often 
impossible  to  say,  from  the  appearance  of  the  precip- 
itate, whether  it  contains  silver  or  not,  and  the  sweet 
taste,  when  it  is  no  longer  strong,  may  be  masked 
by  other  and  less  agreeable  flavors.  I  have  not  been 
able  to  find  a  very  simple  test  for  the  presence  of 
silver  in  this  case,  but  I  will  give  the  one  I  use, 
which  can  be  made  in  ten  minutes. 

126.  The  precipitate  in  the  glass  is  stirred,  or 
shaken,  to  make  it  curdle,  allowed  to  settle  for  a  few 
seconds,  and  a  portion  of  the  liquid  is  poured  off;  the 
remainder,  with  the  precipitate,  is  heated  in  a  small 
porcelain  dish.  The  precipitate  blackens,  shrinks,  and 
settles,  so  that  nearly  all  of  the  liquor  can  be  poured 
off  without  much  loss  of  precipitate.  A  little  nitric 
acid,  and  a  fraction  of  a  grain  of  salt,  are  then  added, 
and  heat  is  again  applied.  The  action  is  very  rapid, 
and  in  a  few  seconds  nothing  remains  of  the  black 
precipitate  but  a  yellow  mass,  principally  sulphur,  but 
possibly  in  part  silver  chloride.  To  prove  this,  ammo- 
nia is  added,  very  cautiously  unless  after  cooling  and 
diluting,  until  the  contents  of  the  dish  smell  strongly 
of  it. 

If  copper  is  present,  it  gives  a  blue  color;  silver 
chloride  is  dissolved  in  the  ammonia,  which  is  then 
poured  upon  a  filter,  and  to  the  liquid  which  passes 

5 


70  SPECIAL    DIRECTIONS GOLD  AND  SILVER. 

through,  and  is  received  in  a  test  tube,  nitric  acid  is 
added,  drop  by  drop,  while  the  test  tube  is  inclined 
away  from  the  operator's  eyes,  until  the  smell  of  am- 
monia is  no  longer  perceptible.  If  there  was  any  silver 
in  the  precipitate,  it  now  appears  as  a  white  cloud  of 
chloride,  which  curdles-  on  being  shaken,  or,  if  in  very 
small  quantity,  as  a  slight  milkiness  in  the  liquid.  A 
little  practice  will  enable  the  operator  to  judge  as  to 
whether  it  is  worth  while  to  continue  the  leaching,  or 
not. 

127.  When  the  quantity  of  silver  in  the  leach  is  incon- 
siderable, the  hypo  is  turned  off,  but,  as  it  is  not  to  be 
wasted,  water  is   again   led  into   the   vat  as  soon  as  the 
ore  is  uncovered,    to   displace   the   hypo   which   would 
otherwise  be  retained.      As  soon  as  it  is   found,  by  the 
taste,  that  the  hypo  is  almost   washed   out,  and    nearly 
pure  water  begins  to   come,  the  stream  is   turned   into 
one  of  the  wash-tubs,  and   the  influx   of  water   to   the 
vat  is  stopped.     The  ore  is  allowed  to   drain,  to   facili- 
tate which  it  may  be   dug  over   with   a  shovel.      It  is 
then  removed. 

128.  The  leaching  of  a  charge  occupies  from  eight 
to    forty-eight    hours,   according   to    the    richness   and 
character  of  the    ore,    and   the   skill    displayed   in   the 
roasting. 

129.  Precipitation  of  Silver. — The  silver  is  precipi- 
tated by  means  of  a   strong  solution  of  calcium   poly- 
sulphide,    called,  in    the*  works,  simply    "calcium,"    or 
"  sulphide,"   which  is  led  into  the  silver  tub,  by    a  hose 
from  the  elevated  vat  in  which   it   is   kept.      It   throws 
down  the  silver,  and  other  metals,  as  sulphides,  in  the 
form  of  a  dark   brown   mud,  which   soon   turns   black. 


SPECIAL   DIRECTIONS — GOLD  AND  SILVER.  71 

At  the  same  time  it  restores  the  hypo,  which  was 
altered  in  dissolving  metals,  so  that  it  can  be  used 
again. 

It  is  imperative  that  not  more  of  the  calcium 
sulphide  be  used  than  the  quantity  required  to  precipi- 
tate the  metals.  If  a  little  silver  remains  in  the  so- 
lution, it  is  not  lost,  as  the  hypo  is  used  again;  therefore, 
it  is  best  to  add  a  Hide  less  of  the  calcium  sulphide  than 
would  be  required  to  precipitate  the  whole  of  the 
metal.  If  too  much  is  used,  the  excess  remains  un- 
changed, and  mixed  with  the  hypo,  in  the  re-use  of 
which  it  converts  some  of  the  silver  chloride  in  the 
ore  into  sulphide,  which  cannot  be  leached  out. 

In  practice  it  is  not  difficult  to  precipitate  aright.  A 
circular  motion  is  given  to  the  solution  in  the  silver 
tub,  the  stream  of  calcium  sulphide  is  turned  in,  and 
allowed  to  run  as  long  as  it  is  seen  to  cause  a  distinct 
precipitation.  The  liquor  is  then  stirred,  thoroughly 
and  vigorously,  for  a  couple  of  minutes.  The  circular 
motion  is  checked  by  a  reversed  movement  of  the 
stirrer;  a  few  minutes  are  allowed  for  partial  settling,  a 
sample  is  taken  in  a  glass,  and  a  little  calcium  sulphide 
added.  If  a  considerable  precipitate  is  produced,  a  few 
more  gallons  of  the  precipitant  are  run  into  the  tub, 
and  the  stirring  and  testing  are  repeated.  When  the 
calcium  sulphide  produces  only  a  very  slight  precipita- 
tion, the  contents  of  the  silver  tub  are  left  undisturbed 
for  a  few  hours. 

130.  If,  in  the  test,  calcium  sulphide  gives  no  pre- 
cipitate, it  may  be  that  too  much  has  been  used  in  the 
tub ;  therefore  another  sample  is  taken,  and  tested  by 
adding  a  few  drops  of  solution  of  iron  sulphate,  which 


72  SPECIAL  DIRECTIONS GOLD  AND  SILVER. 

instantly  gives  a  black  precipitate  if  there  is  the  least 
excess  of  calcium  sulphide.  If  neither  of  the  tests 
gives  a  precipitate,  all  is  right ;  but  if  it  is  found  that 
too  much  calcium  sulphide  has  been  employed,  it  must 
be  counteracted  by  an  addition  of  silver  solution  from 
another  vat,  or,  if  there  is  none  to  be  had,  some  iron 
sulphate  may  be  used  instead.  There  is,  however,  no 
trouble  if  care  be  used.  The  experienced  workman 
knows  almost  the  exact  moment  when  enough  calcium 

o 

sulphide  has  been  added,  by  a  white  cloudiness  which 
appears  in  the  liquor. 

The  precipitate  settles  in  a  few  hours,  and  the  reno- 
vated hypo  is  drawn  off,  by  means  of  an  arrangement 
similar  to  that  used  in  the  gold  tub,  and  pumped  into 
the  elevated  tank,  whence  it  is  again  led  to  the  leaching 
vats  as  required. 

131.  If,  when  the  leaching  of  a  vat  is  finished,  a 
dark  scum  is  seen  on  the  surface  of  the  ore,  it  is  taken 
off  and  returned  to   the   roasting.      It  is  caused   by  a 
small  quantity  of  metal  sulphide,  which   remained  sus- 
pended in  the  hypo  when  it  was  drawn  from   the  silver 
tub,  and  is  thus  filtered  out  by   the   ore.      It  contains 
more  or  less  silver. 

132.  The  metal    contained  in  the  weak  solution  in 
the  wash-tubs,  is  also  precipitated  by  means  of  calcium 
sulphide,  but,  after  the  settling,  the  liquid,  which  is  little 
more   than   water,   is  allowed   to  run   to   waste.     The 
metal   should  be  completely  precipitated,  because,  as 
the  liquid  is  not  used  again,  any  which  might  remain  in 
solution  would  be  lost.     An  excess  of  the  precipitant 
can  do  no  harm  in  this  case. 


SPECIAL    DIRECTIONS GOLD  AND  SILVER.  73 

133.  Collecting  the  Precipitate. — After  several  pre- 
cipitations, or  when  desired,  the  black  mud,  consisting 
of  silver  sulphide,  mixed  with  free  sulphur,  and  more 
or  less  base   metal  sulphide,  is   run   out  through   the 
clean-up  pipe,  faucet,  or  plug-hole,  to  a  filter,  drained, 
washed  by  passing  hot  water  through  it,  again  drained, 
pressed  into  cakes  or  not,  as  desired,  and  dried. 

134.  Roasting  tJie  Precipitate. — The   dried  precipi- 
tate is  next  roasted  in  the  small  reverberatory  furnace, 
to  burn  off  the  greater  part  of  the  sulphur,  beginning 
with    only    the   heat    required    to    set    fire    to   it,  and 
gradually  increasing  the  temperature  to  dark   redness, 
or  to  such  a  degree   as  the  material   will   bear  without 
melting.    It  must  be  stirred  while  roasting,  and  changed 
from  end  to  end  of  the  furnace,  in  the  manner  directed 
for  the   roasting  of  ore.      If  but  little  base   metal   is 
present,    the   roasting   is    continued   until    as    little    as 
possible  of  the  sulphur  remains;  otherwise  a  prolonged 
roasting  is  avoided,  on  account  of  the  formation  of  too 
much  base  metal  sulphate  and  oxide,  which  are  injurious 
to  the  black  lead  pot  in  the  melting. 

13,5.  Melting  the  Silver. — This  is  done  in  black 
lead  crucibles,  in  a  wrind  furnace,  with  coke  or  charcoal 
for  fuel.  If  the  precipitate,  before  roasting,  contained 
but  little  base  metal  sulphide,  the  silver  is  seen  in  the 
form  of  threads  traversing  the  roasted  mass,  which, 
however,  still  retains  a  considerable  quantity  of  sulphur. 
The  crucible,  containing  some  scrap  iron,  is  filled,  and 
placed  in  the  fire,  standing  on  a  piece  of  firebrick;  for 
as  the  melting  occupies  a  considerable  time,  even  a 
thick  layer  of  the  best  coke  does  not  last  long  enough 
to  prevent  the  crucible  from  settling  down  to  the  grate. 


74  SPECIAL    DIRECTIONS GOLD    AND    SILVER. 

A  little  borax  is  added,  and  the  whole  is  heated  till 
there  is  room  in  the  pot  for  more  material,  when  it  is 
refilled  by  means  of  a  scoop  and  funnel.  As  in  the 
case  of  gold,  the  refilling  is  done  before  the  mass'  in 
the  crucible  has  become  fluid,  in  order  to  avoid  loss  by- 
projection.  As  fast  as  the  scrap  iron  disappears,  more 
is  put  in;  but,  if  such  addition  is  made  after  full  fusion, 
the  iron  is  first  heated. 

If  the  roasted  precipitate  contains  much  copper 
or  iron,  more  borax  is  required,  and  a  little  clean 
sand  is  useful,  especially  if  the  roasting  has  been  exces- 
sive. Some  charcoal  is  also  added. 

When  the  pot  is  full  of  thoroughly  melted  mat- 
ter and  pieces  of  iron,  a  test  is  made  by  placing 
the  reel  hot  end  of  a  piece  of  nailrod,  or  thick  iron  wire 
in  it.  If,  after  a  few  minutes,  on  withdrawing  the  rod, 
it  is  found  that  a  part  of  it  has  been  melted,  more  time 
must  be  allowed.  When  iron  is  no  longer  consumed, 
the  melting  of  that  quantity  of  precipitate  is  finished, 
and  slag  and  matte  are  dipped  out,  by  means  of  a  red 
hot  assay  crucible  held  with  the  crooked  tongs,  and 
poured  into  a  mould,  or  iron  pan.  The  pot  is  now 
refilled  with  roasted  precipitate,  taking  the  precaution 
to  add  it  slowly  until  the  melted  mass  is  somewhat 
chilled. 

When  all  the  precipitate  has  been  thus  worked 
up,  or  the  pot  contains  a  sufficient  quantity  of  metal,  a 
part  of  the  slag  and  matte  is  removed  as  before, '  and 
the  remainder,  with  the  silver,  is  poured  into  a  warmed 
and  greased  mould.  The  overflowing  of  the  slag  and 
matte  is  of  no  consequence,  if  the  mould  is  large 
enough  to  contain  the  silver,  which  will  go  to  the  bot- 


SPECIAL    DIRECTIONS GOLD  AND  SILVER.  75 

torn  in  consequence  of  its  greater  specific  gravity. 
After  removal  from  the  mould,  it  is  usual  to  place  the 
bar  in  a  tub  of  water,  for  the  purpose  of  cooling  it,  but 
when  there  is  matte  upon  it  this  must  not  be  done 
until  the  matte  also  has  solidified;  otherwise  an  explo- 
sion will  occur. 

If  the  melting  has  been  properly  conducted, 
the  matte  is  brittle,  and  separates  readily  from  the 
cooled  bar.  If  it  is  tough,  that  which  adheres  to  the 
metal  must  be  beaten  off,  and  the  whole  remelted  in 
presence  of  iron,  as  it  then  contains  a  great  deal  of 
silver.  After  cooling,  it  is  broken  and  examined  for 
any  large  buttons  of  silver  which  may  have  been  dipped 
out  with  it.  All  the  slag  and  matte  is  preserved,  the 
former  to  be  sold,  the  latter  to  be  crushed  and  re- 
worked by  roasting  and  leaching.  If  a  handsome  bar 
is  desired,  it  must  be  remelted  with  borax,  cleaned 
by  skimming,  and  re-cast,  covering  the  surface  with 
powdered  charcoal  before  solidification. 

136.  C. — Concentrations  containing  Silver,  but  little 
or  no  Gold. — These  concentrations    generally    contain 
less  iron  pyrites,  and  more  lead,  zinc,  copper,  antimony, 
and  arsenic,  which  makes  them  more   difficult  to  roast. 
They  require  from  5  to  20  per  cent  of  salt,  according 
to  their  richness.     The  salt  is  usually  charged  with  the 

/  o 

ore,  but  as  some  ores  are   more  liable    to   melt  if  it  is 
added  at  the  commencement  of  the  roasting,  than  if  the 
addition  is  made  at  a  later  period,  it  is  sometimes  neces- 
sary to  complete  the  oxidation,  under  a  moderate  heat 
before  the  salting. 

137.  The  roasting -is  commenced  with  only  the  heat 
required  for  the    ignition   of  the  sulphur.     Stirring  is 


76  SPECIAL    DIRECTIONS — GOLD    AND    SILVER. 

kept  up  almost  continuously,  in  order  to  prevent  sinter- 
ing, or  partial  melting.  If  the  salt  has  not  been  mixed 
with  the  ore  at  the  time  of  charging,  it  is  added  as  soon 
as  the  smell  of  burning  sulphur  has  become  faint,  under 
a  dull  red  heat.  The  heat  is  then  raised  cautiously, 
the  ore  swells,  becomes  flaky,  and  somewhat  sticky,  ap- 
pearing as  though  it  were  moist,  which  is  caused  by 
the  fusing  together  of  the  metal  sulphates  and  the  salt. 

At  this  period  the  ore  must  not  be  stirred  too 
frequently,  or  more  than  is  required  to  ensure  an  equal 
heat,  as  it  facilitates  the  escape  of  chlorine,  which 
should  be  retained  as  long  as  possible  within  the  mass. 
The  furnace  doors  may  be  closed  while  the  stirring  is 
intermitted,  because  what  is  now  required  is  heat  rather 
than  air. 

It  is  a  good  plan  to  heap  the  ore  near  to  the  fire- wall, 
and  let  it  remain  for  a  time,  then  spread  it,  and  again 
gather  it  into  a  heap.  The  roaster  should  be  careful 
to  avoid  pushing  the  somewhat  adhesive  ore  against 
the  wall  of  the  furnace  with  the  hoe.  The  charge 
on  the  finishing  hearth  must  be  changed  from  end  to 
end  at  least  twice;  once  before  the  heat  is  raised,  and 
again  after.  It  is  drawn  out  while  still  giving  off  an 
abundance  of  chlorine  and  volatile  chlorides,  and  is  al- 
lowed to  remain  an  hour  before  being  spread  on  the 
cooling  floor. 

138.  The  degree  of  heat  which  may  be  used  de- 
pends on  the  quality  of  the  ore.  Zincblende  requires 
a  high  temperature  for  its  decomposition.  Iron,  copper 
and  antimony  sulphides,  especially  the  latter,  require  a 
low  heat  at  first,  but  are  not  very  liable  to  cause  sinter- 


SPECIAL    DIRECTIONS GOLD    AND    SILVER.  77 

ing  after  oxidation.  Lead  is  troublesome,  as  all  its 
compounds  are  very  fusible. 

Some  ores  do  not  bear  a  high,  heat,  after  the  ad- 
dition of  salt,  without  a  great  loss  of  silver;  yet  if 
zincblende  is  present  a  strong  heat  is  requisite  for  its 
oxidation.  Such  an  ore  is  roasted  without  salt  until  a 
sample,  ground  in  a  mortar,  and  carefully  horned,  or 
panned,  shows  no  sulphides.  It  is  then  allowed  to 
cool  to  a  moderate  red  heat,  salted  and  mixed.  If  a 
strong  odor  of  chlorine  is  not  thus  developed,  some 
dried  copperas,  in  the  proportion  of  about  sixty  pounds 
to  the  ton  of  ore,  must  be  added  and  mixed.  When 
the  proper  smell  is  obtained,  the  charge  is  withdrawn. 

139.  'Washing  the  Ore. — The  roasted  and  cooled 
ore,  previously  sifted  if  lumpy,  is  placed  in  the  leaching 
vat,  and  cold  water  is  passed  slowly  upward  through 
the  mass,  the  discharge  pipe  having  been  connected 
with  the  water  supply  for  that  purpose.  When  the  vat 
is  full,  the  water  is  admitted  above  the  ore,  and  al- 
lowed to  flow  out  through  the  discharge  pipe.  The 
washings  are  allowed  to  run  to  waste,  unless  they  con- 
tain copper,  in  which  case  they  are  conducted  to  vats 
which  contain  scrap  iron,  by  which  the  copper  is  pre- 
cipitated. 

The  reason  for  introducing  the  water  at  first  in 
the  manner  described  is,  that  a  certain  quantity  of 
silver  chloride  is  dissolved  by  the  strong  solution  of 
base  chlorides  and  residual  salt,  which  is  formed  on  the 
first  introduction  of  water.  By  operating  as  described, 
this  solution  is  brought  above  the  ore,  and  on  being 
diluted  with  a  further  quantity  of  water,  deposits  the 
silver  chloride  in  and  upon  the  ore  mass,  where  it  re- 


78  SPECIAL    DIRECTIONS GOLD    AND    SILVER. 

mains  until  the  hypo  is  admitted,  while  the  major  part 
of  the  base  chlorides,  remaining  dissolved,  is  removed 
by  the  washing. 

A  portion  of  base  metal  chlorides,  however,  is 
also  deposited  "with  the  silver  chloride,  and,  on  this 
account,  some  operators  prefer  to  admit  the  water  at 
once  above  the  ore,  and  to  save  the  silver  which  is  thus 
carried  out,  by  allowing  the  washings  to  flow  through  a 
series  of  launders,  together  with  an  additional  stream 
of  water.  In  the  launders  is  placed  a  quantity  of  wood 
shavings,  or  some  similar  material,  on  and  among  which 
the  silver  chloride,  together  with  base  metal  chlorides, 
is  deposited.  The  shavings,  with  the  metal  chlorides, 
are  then  gathered  up,  and  the  silver  is  extracted,  either 
by  leaching,  or  by  a  smelting  operation  in  a  crucible. 
The  flow  of  water  through  the  ore  is  continued,  until 
a  test  with  calcium  sulphide  gives  no  precipitate. 

140.  If  the  ore  contains  lead  chloride,  it  is  washed 
with  cold  water  until  the  greater  part  of  the  copper 
and  iron  chlorides,  and  salt,  are  removed.  It  is  then 
treated  with  hot  water,  as  long  as  any  metal  can  be 
extracted,  after  which  it  may  be  necessary  to  again 
apply  cold  water,  to  cool  the  ore  before  admitting  the 
hypo,  so  that  too  much  base  metal  may  not  be  ex- 
tracted with  the  silver.  Hot  water,  if  applied  at  first, 
increases  the  solubility  of  silver  chloride  in  the  solution 
of  base  chlorides  and  salt;  but  after  these  are  in  the 
main  removed,  by  means  of  cold  water,  it  may  be  used 
with  advantage.  If,  however,  it  were  immediately  fol- 
lowed by  the  hypo,  more  base  metal  would  be  extracted 
than  would  be  the  case  if  the  ore  were  cooled;  for,  as 
before  remarked,  there  are  base  metal  compounds  in 


SPECIAL    DIRECTIONS GOLD  AND  SILVER.  79 

the  roasted  ore  which  are  insoluble  in  both  hot  and 
cold  water,  but  which  are  soluble  in  the  hypo,  especially 
if  it  is  warm. 

Lead  chloride  is  almost  insoluble  in  cold  water, 
but  dissolves  readily  by  the  aid  of  heat.  The  sul- 
phate is  not  dissolved  by  water,  hot  or  cold. 
Hence  it  is  better  that  lead  should  be  chloridized  in 
the  roasting,  because  it  can  then  be  removed  by  wash- 
ing. If  lead  is  extracted  in  the  silver  leaching,  it  can- 
not, like  copper,  be  retained  in  the  matte  when  melting, 
but  inevitably  goes  into  the  bullion,  because  its  sulphide 
is  easily  reduced  by  iron  at  a  red  heat,  while  the  copper 
sulphide  is  not. 

141.  From  this  point  the  leaching  and  precipitation 
are  carried  on  exactly  as  directed,  after  the  gold  leach- 
ing, for  concentrations  containing  gold  and   silver.      If 
the  ore    contains    a    little  gold,   a  portion  of    it    may 
be  obtained  with  the  silver,   owing  to  the   formation, 
during  the    roasting,  of   the    peculiar    gold    chloride 
described  (30). 

142.  D. — Concentrations  rich    in  Gold  and  Silver^ 
and  containing  much  Lead,  etc.      It  appears  that  certain 
rich  ores,  containing  much  lead,  and   other  obstructive 
metals,  do  not  yield  the  gold  well  when  treated  in  the 
ordinary  way.      To    meet    this  case   Ottokar  Hofman 
has  devised  and  patented  the  following  modification  of 
the  process. 

The  ore  is  subjected  to  a  thorough  chloridizing 
roasting,  then  washed  with  water,  as  described  in  the 
case  of  silver-bearing  concentrations,  leached  for  silver, 
and  again  washed  to  remove  ail  hypo.  It  is  then  re- 
moved from  the  vat,  dried  sufficiently  for  chlorination, 


80  SPECIAL    DIRECTIONS GOLD  AND  SILVER. 

returned  to  the  vat  and  chlorinated.  The  gold  is  then 
leached  out,  and  if  there  still  remains  a  considerable 
quantity  of  silver,  the  ore  is  again  leached  with  hypo 
for  its  extraction.  The  results  are  said  to  be  very  sat- 
isfactory. 

143.  E. — Unconccntr cited  Ore.     This   material,  con- 
taining gold  or  silver,  or  both  gold  and  silver,  is  treated 
in  the  same  way  as  described  for  concentrations  of  sim- 
ilar character,    except   that,   if   it   is   only    moderately 
charged  with  sulphides,  the  furnace  is  made  hotter  be- 
fore being  charged,  and   the  roasting   is   effected  more 
speedily,  and  with  less   draft  in  the   furnace,  "the  rule 
being  only  to  allow  as  much  as  suffices  to  prevent  the 
escape  of  fumes  at  the  doors. 

If,  as  often  happens,  the  ore  contains  too  little 
sulphur  to  effect  the  chloridation  of  silver,  it  is 
necessary,  if  that  metal  is  present,  to  add  a  certain 
quantity,  say  four  or  five  per  cent  of  crushed  pyritous 
ore,  one  per  cent  of  sulphur,  or  from  two  to  three  per 
cent  of  copperas.  The  pyrites  or  sulphur  must  be 
mixed  with  the  ore  before  roasting,  but  copperas  may 
be  put  in  later,  as  described  in  certain  cases  occurring 
in  the  treatment  of  concentrations.  • 

144.  Unconcentrated  ores  are  not  often  treated  for 
gold  by  lixiviation.     They  are  crushed  as  coarsely  as 
is  compatible  with  good  roasting,  but  nevertheless  are 
often  troublesome  to  leach,  on  account  of  clay,  talc,  etc., 
so  that,  while  concentrations  can  be  leached  in  a  bed  of 
from  two  to  four  feet  in  thickness,  without  difficulty,  or 
special  appliances,  unconcentratecl  ores    will,   in  many 
cases,  not  admit  of  more  than   ten   inches,  and,   in   ex- 
treme cases,  they  cannot  be  worked  by  leaching. 


SPECIAL  DIRECTIONS GOLD  AND  SILVER.  81 

This  difficulty  is  sometimes  overcome  by  crushing  the 
ore  in  a  wet  battery.  The  water  removes  the  slimy 
matters  which  impede  filtration,  while  the  heavier  por- 
tion of  the  ore  is  retained  in  "  catchpits."  This  is  in 
fact  a  species  of  concentration,  although  a  very  imper- 
fect one.  As  the  slimes  usually  contain  a  considerable 
quantity  of  silver,  they  must  also  be  preserved,  and, 
since  they  cannot  be  leached,  must  be  treated  in  some 
other  way.  Amalgamation  is  usually  adopted.  On  the 
whole,  the  plan  is  scarcely  to  be  recommended.  In 
cases  of  difficult  leaching  the  suction  pipe,  (54)  may 
be  used. 

145.  When  about  to  begin  leaching  with  the  aid  of 
a  suction  pipe,  it  must  be  filled  with  liquid.  When 
operating  on  ore  which  is  not  chlorinated  with  gas, 
this  is  done  by  connecting  the  pipe  with  the  water  supply, 
and  passing  the  water  upward  through  it,  and  the  ore 
mass,  as  directed  in  beginning  the  washing  of  silver  ore 
(139).  If  a  vent  pipe  (55)  is  in  use,  it  must  be  plugged  as 
soon  as  the  space  below  the  filter  is  full  of  water. 
If  the  ore  has  been  chlorinated  for  gold,  it  is  not 
desirable  to  introduce  the  water  in  this  way,  because 
the  solution  of  gold  would  be  too  much  diluted.  It  is 
then  better  to  let  the  pipe  down  into  the  trough,  and 
stop  the  end  with  a  tight  plug.  On  introducing  water 
into  the  vat,  as  described  in  the  gold  leaching,  it  passes 
through  the  ore,  and,  displacing  the  air,  fills  the  pipe. 
When  the  water  stands  permanently  above  the  ore,  and 
air  bubbles  have  ceased  to  rise,  the  plug  is  removed, 
the  vent  pipe  stopped,  and  the  leaching  is  allowed  to 
proceed,  aided  by  the  weight  of  the  column  of  liquid 
in  the  suction  pipe,  or,  more  correctly,  by  the  pressure 


82  SPECIAL    DIRECTIONS GOLD  AND  SILVER. 

of  a  corresponding  column  of  air.  The  suction  pipe 
may  be  filled  before  charging  the  vat  with  ore,  if  so 
desired,  and  in  the  case  of  silver  ore  the  water  may 
even  rise  to  the  top  of  the  filter,  thus  avoiding  all 
trouble  from  air;  but  when  chlorine  gas  is  to  be  used, 
the  water  must  not  cover  the  aperture  through  which 
the  chlorine  is  admitted. 

To  reduce  friction,  and  give  the  best  effect,  the 
the  suction  pipe  should  be  large;  say,  for  a  ten  foot 
pipe,  one  and  a  half  or  two  inches  in  diameter.  It  is 
impossible  for  it  to  take  air  at  the  lower  end,  with 
either  of  the  arrangments  mentioned,  nor  can  any 
enter  at  the  top  as  long  as  the  vent  pipe  is  closed  and 
there  is  liquid  in  the  vat.  I  have  observed  that  a  fall 
of  six  feet  more  than  doubles  the  flow  of  liquid  through 
a  bed  of  ore  fifteen  inches  deep. 

146.  F. — Ores  Containing  Coarse  Gold,  or  an  Alloy  of 
Gold  and  Silver. — If  the  gold  is  too  coarse,  it  will  not  be 
entirely  dissolved  in  a  single  operation  by  the  above 
described  process  of  chlorination,  or  if  it  is  alloyed  with 
a  considerable  proportion  of  silver,  unless  in  very  fine 
particles,  the  chlorination  may  be  obstructed  by  the 
formation  of  a  crust  of  silver  chloride  on  each  of  the 
particles.  Gold  which  is  too  coarse  is  more  easily  col- 
lected by  amalgamation ;  yet  it  can  be  dissolved  by 
leaching  with  chlorine  water,  that  is,  water  through 
which  chlorine  has  been  passed  until  no  more  is  absorbed. 
An  alloy  of  gold  and  silver  can  be  leached  out  with 
brine  of  common  salt,  saturated  with  chlorine.  The 
chlorine  acts  on  both  of  the  metals,  and  the  brine  dis- 
solves the  chlorides  as  fast  as  they  are  formed.  The 


SPECIAL    DIRECTIONS CALCIUM  POLYSULPHIDE.         83 

dissolved  metals  may  be  precipitated  together,  by  means 
of  plates  of  copper. 

147.  The  Mears  process,  recently  introduced, 
seems  to  be  well  adapted  to  this  class  of  ore.  It  is 
conducted  as  follows  :  The  roasted  ore  is  treated  in 
rotating,  lead  lined,  iron  cylinders,  with  the  addition  of 
water  and  chlorine,  the  latter  being  forced  into  the  cylin- 
ders under  heavy  pressure.  The  gold  is  said  to  be  dis- 
solved very  rapidly,  not  more  than  two  hours  being 
required.  The  pulp  is  then  thrown  into  leaching  vats, 
and  leached  in  the  usual  manner.  An  addition  of  salt 
to  the  charge  in  the  cylinder  would  be  useful  in  case  of 
an  alloy  of  gold  and  silver.  The  advantages  of  apply- 
ing the  chlorine,  or  chlorinated  brine,  under  pressure, 
have  lono-  been  known. 

o 

148.  Calcium  Poly  sulphide. — This  precipitant  for  sil- 
ver is  made  by  boiling  lime  and  sulphur  together  in  water. 
Lime  is  calcium  oxide,  and,  wrhen  boiled  with  sulphur, 
a  part  of  it  is  decomposed;  the  calcium  combines  with 
sulphur,  making  calcium  sulphide,  while  the  oxygen, 
and  ,  some  undecomposed  lime,  combines  with  another 
portion  of  sulphur,  making  calcium  hyposulphite,  which 
is  the  same  as  the  solution  used  in  leaching  silver. 

When  the  solution  of  sulphide  is  used  for  the  pur- 
pose of  precipitation,  the  water  that  it  contains  is  added 
to  the  leaching  solution,  which  would  thus  be  gradually 
diluted  but  for  the  hypo  which  the  precipitant  also 
contains.  This  is  the  reason  why  the  volume  of  the 
leaching  solution  frequently  increases,  notwithstanding 
a  certain  amount  of  waste.  Not  only  is  hypo  formed 
in  making  the  calcium  sulphide,  but  the  sulphide  itself 


84        SPECIAL    DIRECTIONS CALCIUM  POLYSULPHIDE. 

absorbs  oxygen  from  the  air,  and  changes  into  hypo  to 
a  certain  extent. 

Calcium  sulphide  may  be  made  in  an  iron  pot,  over 
a  fire,  with  frequent  stirring.  A  neater  way  is  to  make 
it  in  a  wooden  tub,  using  a  jet  of  steam  for  the  heating. 
It  can  thus  be  made  in  the  vat  in  which  it  is  kept. 
The  vat  is  two-thirds  filled  with  water,  and  steam  is 
admitted.  As  soon  as  the  water  is  hot,  freshly  slaked 
lime  is  mixed  with  it,  and  flowers  of  sulphur  added  by 
rubbing  through  a  sieve.  When  the  sulphide  is 
made  in  this  way,  two  or  three  hours  boiling  suffices. 

149.  The  proportions  of  lime  and  sulphur  vary 
with  the  quality  of  the  lime.  About  1J^  pounds  of 
average  lime  is  required  for  one  pound  of  sulphur; 
75  pounds  of  lime,  50  pounds  of  sulphur,  and  120  gal- 
lons of  water  will  produce  a  solution  of  suitable  strength, 
and  will  suffice  for  the  precipitation  of  from  25  to  50 
pounds  of  silver,  according  to  the  quantity  of  base 
metal  in  the  lixivium.  If  a  direct  fire  is  used  for  the 
boiling,  the  water  which  evaporates  must  be  replaced,  but 
if  steam  is  used,  a  little  less  water  than  the  prescribed 
quantity  should  be  taken,  as  some  will  be  added  by  the 
condensation  of  steam.  It  is  however  to  be  observed, 
that  with  an  insufficient  quantity  of  water,  the  operation 
proceeds  very  slowly.  The  proper  strength  of  the 
solution  is  indicated  by  a  density  of  about  10°  Beaume. 
If  below  6°  it  will  dilute  the  hypo  too  much,  when  used 
for  the  precipitation. 

163.  The  chief  points  to  be  observed  in  making  the 
sulphide  are,  that  the  lime  must  be  slaked  before  use, 
and  must  not  be  in  excess.  If  it  is  not  previously 
slaked,  time  and  material  will  be  wasted.  If  used  in 


SPECIAL   DIRECTIONS — CALCIUM  HYPOSULPHITE.        85 

too  great  proportion,  insoluble  compounds  are  formed, 
or,  at  least,  compounds  which  are  not  sufficiently  solu- 
ble to  be  useful.  An  excess  of  sulphur  is  not  injurious. 
When  the  solution  is  properly  made,  with  good  lime,  it 
is  nearly  of  the  color  of  strong  coffee  ;  it  deposits,  on 
cooling,  few,  if  any,  needle-shaped,  yellow  crystals,  and 
the  residue  consists  only  of  a  small  quantity  of  matter, 
of  a  dirty  greenish  color. 

150.  Calcium  Hyposulphite. — This  solvent  may  be 
made  by  passing  air,  and  the  fumes   from  burning  sul- 
phur, or  from  sulphuric  acid  and  charcoal  heated  in  a 
retort,    through    a    solution    of    calcium     polysulphide 
until  the  latter  is  colorless.      It  is  better  to  buy  a  barrel 
or  two  of   sodium  hyposulphite  in  crystals,  with  which 
to  make  the   leaching  solution  to  begin  with.     In  use, 
with  calcium  sulphide  as  the  precipitant,    the    sodium 
hypo    soon     disappears,    being    replaced  by  calcium 
hypo    through    the    chemical    reactions    which    take 
place. 

151.  The  strength   of  the  solution  to  be  used  for 
leaching  depends  somewhat  on  the  composition  of  the 
ore.      If  this  contains  but  little  base  metal,  the  solution 
may  be  quite  strong,  and  is  even  used  warm.     But,  in 
general,  a  strong  solution  would  extract  too  much  base 
metal.     It   may    be   made  by  dissolving   two    pounds 
of  crystallized  sodium  hyposulphite  in  each  cubic    foot 
of  water,     or   about    26^  .pounds    to     100     gallons. 
I  fit  is  then  found  to  dissolve  too  much   base    metal, 
which    may    be  ascertained    by    an    examination,    or 
an  assay,  of  some  of  the  precipitate,  the   strength  is  re- 
duced by  an  addition  of  water.     After  it  has  been  used 
the  density  cannot  be   relied  on,  as   it  then  contains 


86  SPECIAL    DIRECTIONS WORKING  TEST. 

other  substances  besides  hyposulphite.  A  good  guide  is 
the  taste,  which  should  be  very  sweet  during  the  first 
stage  of  the  leaching,  if  the  ore  contains  much  silver. 
The  solvent  power  of  the  solution  may  at  any  time  be 
tested,  thus:  Dissolve  5.25  grains  of  pure  silver  in 
nitric  acid  ;  precipitate  as  chloride,  by  adding  a  little 
-hydrochloric  acid.  Wash  the  precipitate  three  or  four 
times  with  water,  to  remove  every  trace  of  acid.  One 
fluid-ounce  of  the  leaching  solution  should  dissolve  the 
whole  of  the  silver  chloride.  Some  operators,  when  in 
want  of  leaching  solution  for  silver  ores,  obtain  it  by 
treating  with  calcium  polysulphide  the  solution  of  base 
metal  chlorides  resulting  from  the  preliminary  washing 
of  the  roasted  ore.  The  metals  are  thrown  down  as 
sulphides,  and  the  solution  then  contains  calcium  chlo- 
ride, together  with  the  calcium  hyposulphite  previously 
existing  in  the  precipitant  (148). 

152.  Working  Test. — The  apparatus  used  is  rep- 
resented in  Figure  i,  Plate  6.  The  generator  and 
wash-bottle  are  made  of  two  wide-necked  bottles, 
jars,  or  flasks,  with  corks,  and  some  glass  tubes. 
The  corks  should  be  soaked  in  melted  paraffin, 
and  the  S  tube  is  enlarged  at  the  upper  end,  so  as 
to  form  a  small  funnel,  into  which  to  pour  the  acid.  If 
preferred,  a  glass  generator  and  two-necked  wash-bottle 
can  be  bought  of  J.  Caire,  in  San  Francisco. 

A  chlorinating  vat  is  made  of  a  common  wooden 
pail,  or  small  tub,  in  the  bottom  of  which,  near  the  side, 
a  hole  is  bored  and  a  cork  inserted.  Through  the  cork 
is  passed  a  piece  of  J^-inch  glass  tube  4  inches  long. 
The  cork  and  tube  must  not  project  above  the  bottom  of 
the  pail  inside.  A  wooden  cover  is  made  to  fit  into  the 


Plate 


SPECIAL    DIRECTIONS WORKING  TEST.  87 

pail  half  an  inch  below  the  rim,  and  in  it  is  a  hole,  fitted 
with  a  cork  and  tube  similar  to  those  in  the  bottom. 
The  pail,  while  dry,  is  thoroughly  coated  inside  with 
melted  paraffin,  which  is  caused  to  soak  into  the  wood  a 
little  by  the  aid  of  heat.  A  filter  is  made  in  the  vat  by 
means  of  a  layer  of  pebbles,  covered  with  a  piece  of 
moistened  grain  sack,  or  similar  material. 

A  wejghed  quantity,  from  10  to  20  pounds  of  the 
pulverized  ore,  or  concentrations,  is  dead  roasted 
or  chloridized,  in  a  small  reverberatory  furnace, 
with  the  precautions  indicated,  according  to  the 
character  of  the  ore.  When  cooled,  it  is  slightly 
moistened,  and  thrown  on  the  filter  in  the  vat.  A  space 
of  not  less  than  half  an  inch  must  be  left  between  the 
surface  of  the  ore  and  the  cover,  which  is  now  placed,  and 
luted  with  dough,  or  with  a  paste  made  from  a  mixture 
of  equal  parts  of  flour  and  paris  plaster,  which  will  not 
crack  in  drying. 

Chlorine  is  generated  from  manganese  and  hydro- 
chloric acid,  the  latter  being  more  convenient  for  small 
operations  than  the  sulphuric  acid  and  salt  used  on  the 
large  scale.  Three  ounces  of  manganese  are  put  into 
the  generator,  moistened  with  water,  and  warmed  on  a 
sand  bath  resting  on  a  small  coal-oil  stove.  The  acid  is 
gradually  added  by  means  of  the  S  tube.  The  exit 
tube  of  the  generator  is  connected  with  the  wash-bot- 
tle, and  that  with  the  glass  tube  in  the  bottom  of  the 
vat,  by  rubber  tubing. 

When  a  glass  rod,  dipped  in  ammonia  and  held  to 
the  tube  in  the  cover  of  the  vat,  causes  the  formation 
of  dense  fumes,  indicating  the  escape  of  chlorine,  the 


88  SPECIAL    DIRECTIONS WORKING  TEST. 

surplus  gas  is  conveyed  out  of  the  room  by  a  rubber 
tube  connected  with  the  tube  in  the  cover. 

The  chlorine  is  allowed  to  pass  through  the  ore  for 
an  hour,  more  acid  being  poured  into  the  generator 
when  required,  to  maintain  the  evolution  of  gas.  The 
waste  pipe  is  then  closed  by  a  pinchcock.  The  wash-bot- 
tle is  disconnected  from  the  generator,  but  not  from  the 
vat,  unless  it  is  required  for  another  operation,  in.  which 
case  the  glass  tube  in  the  bottom  of  the  vat  is  effectu- 
ally, and  conveniently,  closed  by  immersing  its  lower 
end  in  melted  stearin,  paraffin,  or  tallow,  contained  in  a 
small  cup  (dry  cup),  which  is  then  allowed  to  congeal. 

Alter  the  lapse  of  from  20  to  40  hours,  as  may  be  re- 
quired, the  cover  is  removed.  A  rubber  tube,  con- 
nected with  the  glass  tube  in  the  bottom  of  the  vat,  is 
arranged  to  deliver  into  a  glass,  or  porcelain  vessel, 
capable  of  containing  about  a  gallon,  and  is  closed  by 
a  pinchcock.  ' 

Water  is  now  sprinkled  on  the  ore,  and  when  the  lat- 
ter has  settled,  more  water  is  poured  in  until  it  is 
covered.  After  half  an  hour,  the  pinchcock  on  the  dis- 
charge pipe  is  adjusted  so  as  to  allow  the  leach  to  flow 
in  a  slow  stream,  water  being  poured  upon  the  ore  from 
time  to  time  to  keep  it  covered.  The  leaching  is  con- 
tinued until  a  sample,  received  in  a  test  tube,  no  longer 
gives  the  slightest  precipitate  on  addition  of  solution  of 
iron  sulphate.  A  more  delicate  test  is  that  with  tin 
protochloride,  which,  with  the  slightest  trace  of  gold, 
gives  a  purple  coloration. 

The  gold  is  precipitated  by  adding  to  the  leach  a 
strong  solution  of  iron  sulphate,  which  is  thoroughly 
mixed  by  stirring  with  a  glass  rod.  To  ascertain  if 


SPECIAL    DIRECTIONS — WORKING  TEST.  89 

enough  of  the  iron  sulphate  to  precipitate  the  whole  of 
the  gold  has  been  used,  a  drop  of  the  liquid  is  trans- 
ferred, by  means  of  the  glass  rod,  to  a  porcelain  dish, 
or  a  saucer,  and  is  brought  into  contact  with  a  drop  of 
solution  of  potassium  ferridcyanide,  or  "red  prussiate 
of  potash."  If  an  intense  blue  coloration  is  not  pro- 
duced, more  iron  sulphate  is  required. 

The  gold  requires  12  hours  to  settle,  after  which  the 
greater  part  of  the  clear  liquid  may  be  removed  by 
means  of  one  of  the  rubber  tubes,  applied  as  a  siphon. 
The  remainder,  with  the  gold,  is  thrown  on  a  paper  fil- 
ter, or  the  whole  of  the  liquid  may  be  passed  through 
the  filter,  to  insure  the  collection  of  every  particle  of 
the  metal. 

The  sides,  and  bottom  of  the  vessel  in  which  the  pre- 
cipitation was  effected,  and  the  glass  rod  with  which  the 
stirring  was  performed,  are  carefully  wiped  with  pieces 
of  filter  paper,  held  in  the  forceps,  to  remove  adhering 
gold,  and  the  paper  is  added  to  the  gold  on  the  filter. 
The  filter,  with  the  metal,  is  dried  in  the  funnel,  and  is 
then  placed  in  an  assay  crucible,  together  with  an 
ounce  or  more  of  litharge,  and  a  little  borax,  and 
smelted.  The  filter  reduces  a  sufficient  quantity  of 
litharge  to  metallic  lead,  for  the  collection  of  the  gold, 
which  is  then  separated  by  cupellation,  weighed,  and 
the  result  compared  with  the  assay  of  the  ore. 

If  the  ore  contains  silver,  the  gold  on  the  filter  may 
be  washed  with  water,  then,  with  the  entire  filter, 
drenched  with  ammonia,  and  again  washed,  before 
being  dried.  This  will  remove  any  silver  chloride 
which  may  be  present,  or  the  bead  may  be  inquartated 
and  parted  in  the  usual  way.  After  the  extraction  of 


90  SPECIAL    DIRECTIONS WORKING  TEST. 

the  gold,  the  ore,  which  in  this  case  should  have  been 
roasted  with  salt,  is  leached  with  hypo  for  silver  as  long 
as  a  precipitate  is  produced  by  the  addition  of  a  drop 
of  calcium  sulphide  to  a  sample  of  the  leach. 

The  silver  is  then  precipitated  with  calcium  sulphide, 
as  in  the  large  way,  except  that,  as  it  is  not  necessary  to 
preserve  the  hypo,  an  excess  of  the  sulphide  is  used,  so 
that  not  a  trace  of  the  metal  may  be  lost.  The  precipi- 
tate is  coagulated  by  heating  on  a  sandbath,  separated 
from  the  liquid  by  filtration,  dried,  and  dressed  on  the 
filter  with  litharge  and  borax,  then  fused  in  a  crucible, 
with  the  addition  of  a  little  nitre  to  prevent  the  pro- 
duction of  too  much  lead  by  the  action  of  the  sulphur 
on  litharge.  The  lead  button  obtained  is  cupelled,  and 
the  resulting  silver  bead,  after  weighing,  should  be  sub- 
jected to  parting,  as  it  may  contain  a  little  gold. 

The  tailings  are  dried  and  weighed.  The  loss  of 
weight  found  to  have  been  sustained  by  the  ore  in  the 
working  is  reduced  to  percentage.  An  assay  of  the 
tailings  is  then  made,  and  from  the  result  the  same  per- 
centage is  deducted.  The  remainder  is  the  loss  per 
ton  of  ore  by  insolubility.  This  is  added  to  the 
amount  per  ton  extracted,  and  the  sum  deducted  from 
the  assay  value  of  the  original  ore.  The  remainder  is 
the  loss  per  ton  by  volatilization,  dusting,  and  other 
causes. 

153.  A  smaller  test  may  be  made  in  the  laboratory. 
Half  an  ounce,  or  an  ounce,  of  ore,  is  roasted  in  the 
muffle,  with  the  precautions  indicated  under  "  Assay- 
ing Concentrations"  (160),  with  or  without  salt,  as  re- 
quired, and  is  chlorinated  in  the  apparatus  represented 
in  Fig.  2,  Plate  6,  formed  of  two  glass  funnels.  In  the 


SPECIAL  DIRECTIONS CHANGE  IN  WEIGHT.  91 

neck  of  the  lower  funnel  some  fragments  of  broken  glass 
are  placed,  and  on  them  a  filter  is  constructed  of  rather 
coarsely  powdered  glass.  Upon  the  filter  the  moist- 
ened ore  is  placed,  the  upper  funnel  is  then  arranged 
as  a  cover,  and  luted  with  a  paste  of  flour  and  paris  plaster. 
Two  ore  sample  bottles,  fitted  with  corks  and  tubes, 
as  in  Figure  i,  suffice  for  a  generator  and  wash  bottle. 
The  corks  should  be  saturated  with  paraffin  or  tal- 
low. 

This  operation  has  the  advantage  that,  after  the 
precious  metal  has  been  extracted  and  collected,  as  in 
the  larger  test,  the  whole  of  the  ore  and  glass  filter, 
dried  in  the  funnel,  can  be  dressed  as  an  assay  and 
smelted,  so  that  it  not  only  shows  what  can  be  extracted, 
but  it  also  gives  the  absolute  loss  by  insolubility,  and, 
by  difference,  the  loss  in  roasting,  without  complications 
arising  from  a  change  of  weight  in  working, 

154,  Change  in  Weight.  When  working  on  the  large 
scale  by  lixiviation,  it  must  be  remembered  that  the  ore 
not  only  gains  or  loses  weight  in  the  roasting,  but  also 
loses  in  the  leaching  by  the  amount  of  soluble  matter,  of 
whatever  kind,  extracted.  The  tailings  assay,  therefore, 
does  not  represent  the  real  loss  by  insolubility  unless 
corrected.  The  change  of  weight  sustained  in  roasting 
and  leaching,  is  approximatively  obtained  by  weighing, 
roasting,  leaching,  drying,  and  reweighing  a  number  of 
small  samples,  using  the  same  proportion  of  salt, 
and,  as  nearly  as  possible,  the  same  heat  in  roast- 
ing, as  in  the  large  way.  The  loss  of  weight  thus 
found,  when  reduced  to  percentage,  gives  the  correc- 
tion to  be  applied  to  the  assay  value  of  the  tailings. 
Thus,  if  tailings  assay  2.6  oz.  per  ton,  and  the  loss  of 


92  SPECIAL    DIRECTIONS — LOSS  IN  ROASTING. 

weight  in  roasting  and  leaching  has  been  found  to 
average  22  per  cent,  the  real  loss  per  ton  of  crude  ore, 
from  insolubility,  is  2.6 — 0.57=2.03  oz. 

155.  Loss  in  Roasting. — The  only  reliable  method 
of  determining  the  loss  of  gold  or  silver  in  the  roast- 
ing of  ore  on  the  large  scale  is,  to  dry,  weigh,  sample, 
and  roast  a  quantity,  say  from  one  to  ten  tons;  then,  after 
cooling,  to  weigh  and  sample  again.  It  may  weigh 
more  or  less  than  before,  according  to  the  character 
of  the  ore,  the  quantity  of  salt  used,  and  the  manner  of 
roasting.  The  assay  of  the  unroasted  ore,  coupled 
with  the  total  weight  taken,  gives  the  quantity  of 
precious  metal  in  the  lot  before  roasting,  and  the  assay 
of  the  roasted  ore,  with  its  total  weight,  gives  the  quan- 
tity remaining  after  roasting.  The  difference  is  the 
loss,  caused  by  dusting  and  volatilization.  To  make 
the  test  reliable,  the  furnace  must  be  thoroughly 
cleaned,  both  before  and  after  the  roasting ;  if  this  is 
neglected,  the  weight  obtained  for  the  roasted  ore  will 
be  incorrect. 

As  a  part  of  the  precious  metal  lost  in  the  roasting 
may  be  recovered  from  the  flues  and  dust  chamber, 
while,  besides  the  losses  already  discussed,  others  may 
occur  in  the  leaching,  collecting,  and  melting  of  the 
metal,  it  will  be  seen  that  a  final  result  can  only  be 
reached  by  means  of  a  general  and  complete  clean-up ; 
yet,  as  this  cannot  be  had  very  frequently,  the  investi- 
gations described  are  indispensable  as  guides  in  work- 
ing. 

It  is  best,  when  any  doubt  is  entertained  as  to  the 
best  way  of  roasting  a  given  ore,  to  experiment  in  the 
laboratory  on  ounce  or  half  ounce  samples  taken  from 


SPECIAL    DIRECTIONS  -  -SOLUBILITY  ASSAY.  93 

crushed  lots  of  considerable  magnitude.  The  method 
employed  by  some  metallurgists,  of  taking  samples  from 
the  furnace  at  intervals  during  the  progress  of  the  roast- 
ing, and  assaying  them  with  the  view  of  ascertaining  the 
loss  at  successive  stages,  is  open  to  the  objection  that 
it  cannot  be  known  exactly  what  correction  must  be 
made  for  the  changes  of  weight  sustained  by  the  ore. 
It  is,  however,  very  proper  to  make  such  trials,  because 
a  heavy  loss  might  be  thus  indicated  in  time  to  alter 
the  treatment  of  the  charge.  The  percentage  of  the 
silver  which  is  soluble  must  be  considered  in  connec- 
tion with  the  loss  by  volatilization,  in  order  to  arrive  at 
the  most  profitable  manner  of  roasting ;  for  it  is  better 
to  make  rich,  rather  than  poor,  tailings,  if  the  difference 
should  go  up  the  smoke  stack. 

156.  Solubility  Assay. — This  is  commonly,  but  in- 
correctly, called  a  "  chlorination  assay."  It  is  made  as 
follows  :  From  a  quantity  of  the  roasted  ore,  two 
assays  are  weighed  out,  one  of  which  is  leached  on  a 
filter  with  hypo  as  long  as  any  metal  can  be  detected 
in  the  filtrate ;  it  is  then  washed  and  dried.  The 
leached  and  the  unleached  samples  are  then  separately 
smelted,  -and  the  resulting  lead  buttons  cupelled  and 
parted.  The  result  obtained  from  the  unleached  sam- 
ple gives  the  assay  value  of  the  roasted  ore ;  that  from 
the  leached  sample  the  portion  of  the  silver  which  is 
insoluble  in  hypo. 

If  the  average  change  of  weight  which  the  ore  sus- 
tains in  roasting  has  been  ascertained,  a  corresponding 
correction,  applied  to  these  assays,  will  show  the  loss 
in  roasting,  if  an  assay  has  been  made  of  the  unroasted 
ore ;  thus  : 


/7-  -    2  /ff; 


94  SPECIAL    DIRECTIONS — SOLUBIL 

Raw  ore  contains  56  oz.  of  silver  per  ton. 
Loss  of  weight     in    roasting=5    per  cent;  therefore, 
Roasted  ore  should  contain  56  +  2.9=58.9  oz.  per  ton, 
but  actually  contains          57.0    "     "      " 

The  loss  in  roasting   is   therefore       1.9    "     "      " 

Unleached  sample  contains  57  oz.  per  ton 
Leached  "  "          1.5   "     "     " 


Soluble  silver  55.5  •'     "     "       =97-3 

cent  of  the  silver  remaining  in  the  ore  after  roasting. 
But  a  ton  of  roasted  ore  which  has  lost  5  per  cent  in 
weight  corresponds  to  1.052  ton  of  raw  ore,  containing 
58.91  oz.  of  silver,  of  which  we  extract  55.5  oz.  The 
total  loss  therefore  is  3.41  oz.,  in  58.91  oz.,  or  5.79 
per  cent  nearly,  which,  however,  would  be  a  better  re- 
sult than  is  often  obtained. 

PLAN  OF  WORKS. 

157.  Plate  7  will  give  the  reader  a  good  idea  of 
the  general  arrangement  of  a  plant  for  treating,  per  day 
of  24  hours,  from  i  ^  to  3  tons  of  concentrations  con- 
taining gold  and  silver.  The  appended  description 
will  also  serve  as  an  inventory  of  the  principal  articles 
required  : 

A — Two  hearth  roasting  furnace  ;  A  A! — The  same 
extended  to  three  hearths  ;  B — Drier  ;  C — Smoke 
stack  ;  D — Floor,  level  with  top  of  drier,  with  store- 
room beneath;  E — Hopper;  F — Boiler,  for  heating  pur- 
poses, set  in  flue;  G — Passage  way  under  flue  ;  H — 


Plate  WL 


Plan  of  Works. 


PLAN  OF  WORKS.  95 

Melting  furnace  ;  k — (dotted)  Small  roasting  and  dry- 
ing furnace  for  precipitate— inside  drier  ;  / — Sheet-iron 
muffle  for  drying  gold  ;  m — Assay  furnace  ;  n — Door- 
way to  laboratory  ;  o — Steps  to  lower  floor  ;  / — Tank 
for  hypo  ;  q  q  q  q — Leaching  vats ;  r  r — Silver  precipi- 
tating tubs  ;  s — Calcium  sulphide  vat;  t — Well  and 
pump  ;  u  u  ^l — Filters  for  precipitate  ;  v  v — Gold  pre- 
cipitating tubs;  w — Iron  sulphate  vat;  x — Small  tub 
to  receive  washings  from  vv;  y — Filter  tub  for  waste 
solution  ;  z — Gasometer,  or  blower  ;  a — Chlorine 
generator  ;  b — Wash-bottle  ;  c  c — Cars  for  removing 
tailings  ;  d  d — Tram-ways,  6  feet  above  floor ;  e — 
Press  for  silver  precipitate. 


ASSAYING  CONCENTRATIONS 


158.  It  is  well  known  that  many  experienced  as- 
sayers,  although  generally  reliable,  do  not  obtain  cor- 
rect results  from  the  assay  of  gold-bearing  sulphides, 
very  rich  ores  of  silver,  or  cement  copper  containing 
gold,  and  contaminated  by  basic  chlorides.  A  few 
facts  and  suggestions  on  this  subject  may  not  be  out  of 
place  here.  As  this  is  not  a  treatise  on  assaying,  the 
reader  is  supposed  to  be  familiar  with  the  apparatus 
and  manipulations  to  be  employed. 

A  common  practice  among  assayers,  and  by  some 
deemed  indispensable,  is  to  roast  the  assay  of  gold- 
bearing  sulphides.  It  is  better  not  to  do  so  unless 
they  contain  much  arsenic,  and  even  in  that  case,  scori- 
fication  is  preferable. 

When  an  accurate  assay  of  an  ore  which  is  new  to 
the  assayer  is  desired,  it  is  best  to  make  several  assays 
by  different  methods.  If  the  assayer  knows  how  to 
properly  clear,  weigh,  and  part  the  bead,  and  to  make 
the  necessary  allowance  for  silver  in  the  litharge  or 
lead  employed,  the  presumption  of  correctness  is  in 
favor  of  the  highest  result,  because,  although  it  is  easy 
to  lose  gold  or  silver  in  an  assay,  it  is  impossible  to  ex- 
tract more  than  the  ore  contains.  In  important  as- 
says, such  as  those  on  which  the  purchase  of  a  lot  of 
ore  is  based,  the  carefully  taken  sample  should  be 
thoroughly  dried  at  the  heat  of  boiling  water,  passed 
through  a  seive  of  at  least  80  meshes  to  the  run- 
ning inch,  and  then  very  carefully  mixed. 


98  ASSAYING  CONCENTRATIONS. 

It  is  generally  assumed,  and  so  implied  in  books  on 
the  subject,  that  if  two  assays,  made  at  the  same  time, 
and  in  the  same  manner,  give  correspondiug  results, 
they  are  correct.  This  is  a  great  mistake.  Two 
chemical  operations  conducted  under  precisely  similar 
conditions  should  give  similar  results.  Their  agree- 
ment proves  that  no  accidental  loss  has  occurred,  nor 
any  error  in  weighing,  but  it  does  not  prove  that  the 
method  adopted  is  that  by  which  the  highest  results 
can  be  obtained. 

159.  There  are  two  principal  methods  of  assaying 
ores  for  gold  and  silver — by  crucible,  and  by  scorifica- 
tion.  The  crucible  assays  may  be  divided  into  two 
classes;  firstly,  that  in  which  a  thoroughly  oxidized  slag 
is  produced ;  secondly,  that  in  which  a  matte  contain- 
ing the  minimum  proportion  of  sulphur  is  formed. 

The  scorified  assay  is  always  a  completely  oxidized 
assay,  and  is  the  most  certain  in  its  results,  but  is  sub- 
ject to  certain  inconveniences.  Either  a  very  small 
quantity  of  ore  is  operated  on,  or,  a  very  large  quantity 
of  lead  is  obtained,  and  it  usually  requires  more  time 
than  a  crucible  assay.  Yet  it  is  indispensable  as  a 
check,  for  in  some  cases  it  gives  higher  results  than 
can  be  obtained  from  the  crucible,  especially  with  some 
arsenical  compounds. 

Each  kind  of  assay  is  subject  to  modifications  as  to 
the  quantity,  kind,  and  respective  proportions  of  fluxes 
used,  depending  on  the  constituents  of  the  ore  ;  whence 
it  is  difficult  to  give  rules  to  meet  the  requirements  of 
all  cases. 

Concentrated  gold  bearing  sulphides,  chiefly  iron 
pyrites,  with  or  without  an  admixture  of  other  sul- 


ASSAYING    CONCENTRATIONS.  99 

phides  containing   silver,  are  assayed  by  the  different 
methods  as  foilows  : 

160.  ist  Assay. — Half  an  ounce  of  the  finely  pulver- 
ized and  dried  ore  is  roasted  in  a  roasting  dish,  in  the 
muffle.  To  prevent  loss  by  decrepitation,  the  assay  is 
covered  by  another  roasting  dish  inverted.  A  small 
hole  should  be  bored  through  the  cover,  and  a  few 
notches  broken  in  its  edge,  so  that  the  arrangement 
resembles  a  small  reverberatory  furnace. 

The  heat  is  kept  very  low,  and  after  a  time  the  dish 
is  taken  from  the  muffle  and  cooled  a  little,  to  prevent 
decrepitation,  and  consequent  loss,  on  uncovering  it. 
The  cover  is  then  removed,  and  the  ore  well  stirred 
and  turned  over,  again  covered,  and  returned  to  the 
muffle.  This  is  repeated  until  it  is  found  that  the  assay 
may  be  uncovered  and  stirred  within  the  muffle,  with- 
out danger  of  loss  by  decrepitation.  The  heat  is  then 
increased  to  bright  redness,  and  so  maintained  until  the 
ore  is  odorless.  After  cooling,  the  assay  is  dressed 
thus  : 

Ore  (roasted) 

Litharge 2  to  4  ounces 

Sodium  bicarbonate ^2 

Flour 40  grains. 

Mix,  and  place  in  a  No.  8  French  crucible,  containing 
YZ  ounce  of  borax  in  crystals,  and  cover  with  salt. 
Fuse  quickly  in  a  strong  fire.  Allow  the  assay  to 
remain  five  minutes  in  the  fire  after  fusion,  and  pour. 
The  lead  button  should  weigh  about  300  grains.  If 
it  varies  much  from  that  weight,  the  assay  should  be 
repeated,  with  a  larger  or  smaller  quantity  of  flour  as 


100  ASSAYING    CONCENTRATIONS. 

the  case  may  be.  A  duplicate  assay  should  be  made, 
with  either  more  or  less  litharge,  as  a  check.  The 
lead  buttons  are  cupelled  as  usual. 

161.  2d  Assay:— 

,   Ore  (not  roasted) .  . ^         ounce  c 

Litharge 2  to  4      " 

\    Sodium  bicarb y£  " 

Dried  borax .  y2 

V  Pulverized  nitre 420  grains.  - 

Mix  ;  put  into  a  No.  8  French  crucible,  and  cover  with 
salt.  Heat  the  assay  very  slowly  until  fused;  raise  the 
heat  to  bright  redness,  and  keep  it  so  for  five  minutes 
at  least ;  then  pour. 

The  button  should  weigh  about  300  grains,  and 
be  soft.  No  matte  should  be  formed.  If  these  con- 
ditions are  not  fulfilled  the  assay  is  imperfect,  and  must 
be  repeated  with  a  different  proportion  of  nitre,  more 
if  the  button  is  too  large,  or  if  a  matte  is  formed;  less 
if  it  is  too  small.  Theoretically,  25  parts  of  nitre  con- 
vert 100  parts  of  lead  into  litharge;  in  practice  the  pro- 
portion varies  with  the  purity  of  the  nitre. 

162.  sd  Assay.  - 

Ore y±         ounce 

Litharge 2  to  4       " 

Sodium  bicarb ]/% 

Dried  borax ^2 

Pulverized  nitre • 300  grains. 

Place  the  mixture  in  a  No.  8  crucible ;  cover  with 
salt ;  fuse  very  slowly.  When  ebullition  ceases,  under 
a  good  red  heat,  add  20  grains  of  charcoal  in  lumps,  a 
portion  at  a  time.  When  the  evolution  of  gas  pro- 


ASSAYING    CONCENTRATIONS.  101 

duced  by  the  charcoal  ceases,  cover,  and  heat  strongly 
for  ten  minutes ;  then  seize  the  crucible  with  the 
tongs  and  shake  it,  without  removal  from  the  fire. 
Again  cover,  and  leave  it  in  the  fire  for  a  few  minutes 
longer,  and  pour. 

In  this  assay,  the  quantity  of  nitre  is  sufficient  for 
the  complete  oxidation  of  even  pure  iron  pyrites. 
Any  excess  is  decomposed  by  the  heat,  and  after  its 
decomposition  the  addition  of  20  grains  of  carbon  gen- 
erally reduces  a  suitable  quantity  of  lead,  which,  for  120 
grains  of  ore,  is  about  150  grains.  If  it  does  not,  the 
carbon  alone  is  varied.  The  method  is  a  little  tedious, 
but  gives  very  good  results,  especially  as  to  gold. 

163.  In  all  the  preceding  assays  the  crucible  is  lia- 
ble to  extensive  corrosion,  unless  the  ore  contains  a  con- 
siderable quantity  of  quartz.     This  may  be  prevented 
by  the  addition  of  half  or  a  whole  teaspoonful  of  pul- 
verized quartz,   which   must  of  course    be    free    from 
precious  metal.     Glass  will  answer  the  purpose,    but 
rather  more  of  it  is  required. 

1 64.  An  assay  which  is  dressed  with  undried  borax 
is  less  liable  to  boil  over  if  put  at  once  into  an  intense 
fire,  than  if  heated  by  slow  degrees.     When  nitre  is 
used    rapid  heating  is  not  admissible,  hence  the  borax 
is  dried  before  use.      It  is  well  to   dry   it  in  all   cases. 
Boiling  over  sometimes  occurs  in  consequence  of  an  evo- 
lution of  carbonic  acid  gas  (carbon  dioxide)  produced  by 
the  fusion  of  the  alkaline  carbonate,  used  as  a  flux,  with 
silica.     A  large  proportion  of  litharge,  and  less  of  the 
carbonate,   will  correct   this,  while  forming  an    equally 
good  slag.     Whenever  the  assay  tends  to  boil  over,  it 
may  be  cooled  clown  by  throwing  a  little  dry  salt  into  it. 


102  ASSAYING    CONCENTRATIONS. 

165.  4th  Assay.— 

Ore 1 20  grains. 

Litharge 6000       " 

Cover  with  salt;  fuse  quickly,  and  pour  as  soon  as 
the  assay  becomes  quiet.  The  lead  button  should 
weigh  about  two  ounces,  if  the  ore  consists  chiefly  of 
iron  pyrites.  It  must  be  reduced  by  scorification  to  a 
suitable  size  for  the  cupel. 

166.  ^th  Assay.- 

Ore y2  ounce. 

Sodium   bicarb 720  grains. 

Litharge 300       " 

A  little  flour  and  pulverized  glass  will  do  no  harm, 
and  in  some  cases  are  beneficial.  Place  in  a  No.  7  or  8 
crucible,  with  a  very  little  borax  and  three  large  nails ; 
cover  with  salt.  Fuse  slowly;  then  give  a  white  heat 
for  half  an  hour  or  more.  If,  on  seizing  one  of  the 
nails  with  the  tongs,  rinsing  it  in  the  fluid  slag,  and 
tapping  it  against  the  side  of  the  pot,  it  is  found  to  be 
free  from  adhering  lead  globules,  the  other  nails  may 
also  be  removed;  but  if  the  nail  shows  adhering  lead, 
which  cannot  be  washed  off,  more  time  is  required. 

The  matte  and  slag  should  retain  no  lead  in  any 
form;  hence  the  weight  of  the  button  should  correspond 
writh  that  of  the  litharge  used,  or  may  be  in  excess,  if 
the  ore  contained  lead.  It  must  be  soft,  and  separate 
well  from  the  matte.  If  it  does  not,  more  soda  is 
probably  required.  300  grains  of  pure  litharge  con- 
tain 278.5  grains  of  lead,  but  five  per  cent  may  be 
allowed  for  volatilization. 

This  is  a  very  convenient  assay,  requiring  but  little 
modification  for  the  different  sulphuretted  ores.  It  is 


ASSAYING  CONCENTRATIONS.  103 

not  liable  to  boil  over,  nor  is '  it  so  destructive  to  the 
crucible  as  are  the  other  methods  described.  If  properly 
made,  it  gives  as  high  results  as  can  be  obtained  by  any 
other  method,  in  most  cases,  both  as  to  gold  and  silver. 
Arsenical  mattes  cannot  be  assayed  successfully  by 
this  method,  and,  in  one  instance  of  gold  and  silver 
bearing  sulphides,  though  it  gave  the  gold  correctly,  it 
did  not  yield  as  much  of  the  silver  as  the  assay  by 
scorification. 

167.  Oxidized  coppery  ores,  and  especially  cement 
copper  contaminated  with  basic  chlorides,  may  be  con- 
veniently assayed  for  gold  and  silver  by  a  similar  pro- 
cess, as  follows: 

Ore  or  cement  copper J/£  ounce. 

Sodium  bicarb 720  grains. 

Litharge 300      " 

Some  flour,  or  charcoal,  borax,  and  enough  sulphur 
to  convert  all  the  copper,  the  sodium,  and  the  lead  from 
the  litharge,  into  sulphides.  An  excess  of  sulphur  does 
no  harm.  The  mixture,  covered  as  usual  with  salt,  is 
first  fused;  the  nails  are  added,  and  a  strong  heat  is 
continued  for  half  an  hour.  The  copper  remains  in 
the  state  of  matte;  the  nails  reduce  the  lead  sulphide, 
and  take  up  all  excess  of  sulphur.  Massive  copper, 
and  other  metals,  may  be  treated  in  the  same  way,  if 
first  broken,  or  cut  into  fragments. 

168.  6th  Assay. — Scorification. — 

Ore 60  grains. 

Granulated  lead 480        " 

Mix  in  a  scorifier,  and  cover  with  another  ounce  of 
granulated  lead.  Place  the  scorifier  in  the  muffie,  under 
a  low  heat,  and  increase  the  temperature  gradually,  until 


104  ASSAYING  CONCENTRATIONS. 

the  "  bull's  eye  "  appears — that  is,  until  the  surface  of 
the  melted  lead  is  clear  in  the  centre,  and  the  fused,  or 
partly  fused,  ore  forms  a  ring  around  it.  Keep  up  a 
cupelling  heat,  until  the  slag  quite  covers  the  lead,  then, 
with  the  tongs,  add  some  lumps  of  borax,  and  give  a 
strong  heat.  Stir  with  a  red  hot  piece  of  stout  iron 
wire,  to  detach  pasty  lumps  from  the  side  of  the 
scorifier.  Pour  when  the  sla^  has  become  so  fluid  as 

O 

to  run  completely  ofTthe  stirrer.  If  the  lead  button  is 
too  large,  return  it  to  the  scorifier,  after  detaching  the 
cooled  slag,  and  oxidize  it  until  of  the  proper  weight. 

169.  Nearly  clean   silver   glance    is    conveniently- 
assayed  by  mixing  it  with  two  or  three  parts  of  litharge, 
melting   quickly,   and  pouring  as  soon  as  well  fused. 
The  assay  No.  5  is  well  adapted  to  heavily  sulphuretted 
silver  ores,  containing  antimony,  arsenic,  and  zinc,  as 
well  as  copper.      It  is  rarely  necessary  to  roast   silver 
ore  for  assaying. 

170.  In    assaying    rich    silver    ores,     that    part  of 
the  cupel  which  is  saturated  with  the  lead  oxide   must 
be  pulverized,  dressed  with  litharge  and  flour,  smelted, 
and  the  resulting  lead  cupelled,  as  a  considerable  quan- 
tity of  silver  is  thus  added  to  the  result.      This  is  quite 
important. 

171.  Tailings   of  concentrated   and   roasted   gold- 
bearing  sulphides  are  treated  precisely  as  No.  i,  omit- 
ing  the   roasting.     The  reason   why    as   much    as   40 
grains    of    flour  must  be  used     in  an     assay  of    240 
grains  of  the  roasted  ore  is,  that  the  iron  peroxide  which 
it  contains  consumes  the  carbonaceous   matter,  being 
reduced  to  protoxide,  and  if  only  the  usual  quantity  of 
the  reducing  agent  were  used,  little  or  no  lead  would 
be  produced. 


ADDENDA. 


FLUE    COVERING. 

172.  A  very  convenient  covering  for  horizontal 
flues,  which  can  be  removed  and  replaced  easily,  is 
shown  in  the  annexed  diagram.  It  consists  of  a  kind  of 

arched  tile,  made  by 
binding  together,  with 
an  iron  clamp,  as  many 
bricks  as  may  be  re- 
quired by  the  width  of  the  flue,  each  tile,  or  section, 
having  the  length  of  one  brick.  The  flue  is  covered 
with  these  sections,  and  the  interstices  are  filled  with 
mortar,  or  a  mixture  of  clay  and  sand. 


FILTERS. 

173.  Filters  for  dumping  vats  are  made  with  a  bed 
of  twigs,  in  place  of  gravel,  and  over  the  twigs  is  a 
piece  of  cloth,  which  is  held  close  to  the  inner  surface 
of  the  staves  by  a  wooden  hoop.  The  objection  to 
burlap  or  other  cloth  is,  that  it  is  speedily  destroyed  by 
chlorine  gas.  Attempts  have  been  made  to  preserve 
it,  by  soaking  it  in  coal  tar  and  asphalt,  but  without 
much  success.  It  occurred  to  me  to  use  asbestos  cloth, 
but  I  found  none  that  was  not  too  closely  woven.  Clay 
tiles,  of  the  kind  known  as  "  biscuit  ware,"  have  been 
suggested  for  filters,  and  it  may  be  that  basket  work, 
made  of  rattan,  would  answer,  especially  if  soaked  in 
petroleum,  or  ozokerite. 


106  ADDENDA. 

COPPER. 

174.  When  concentrations  which  are  to  be  chlori- 
nated for  gold,  contain  also  copper,  the  roasting  is  not 
pushed  to  the  decomposition  of  copper  sulphate.  The 
latter  is  converted  into  chloride  by  an  addition  of  salt, 
a  short  time  before  discharging  the  ore  from  the  fur- 
nace. The  leach  is  then  green,  and,  after  precipitating 
and  settling  the  gold,  it  is  drawn  off,  either  through  a 
filter  or  not,  as  desired,  and  led  into  tanks  containing 
iron,  where  it  is  allowed  to  stand  until  the  tanks  are 
again  required.  The  iron  goes  into  solution,  and  the 
copper  is  precipitated  in  the  form  known  as  "cement 
copper,"  which  is  collected  periodically,  washed  on  a 
filter,  with  hot  acidulated  water,  dried  and  sold.  As  it 
may  contain  gold  it  should  be  assayed  for  that  metal. 


MEANS      OF      DRAWING     LIQUID     FROM 
PRECIPITATING    VATS. 

175.  Some  operators  use  wooden  faucets  for  this 
purpose.  One  objection  to  faucets  is,  that  a  portion  of 
the  precipitated  gold  lodges  in  the  bore,  and  it  is  neces- 
sary, on  opening  the  faucet,  to  place  a  bucket  under  it 
to  receive  the  first  liquid  which  flows.  Faucets  often 
give  trouble  by  leaking,  especially  when  used  for  metal- 
lic solutions,  which  have  a  tendency  to  cause  wood  to 
shrink.  Plugs  are  also  objectionable  on  account  of 
their  liability  to  leak.  If  used  they  must  fit  flush  with 
the  inside  of  the  tub. 

A  piece  of  rubber  hose,  applied  as  a  syphon,  answers 
very  well,  if  prevented  from  drawing  too  near  the  bot- 


ADDENDA.  107 

torn  of  the  vat,  by  fastening  a  strip  of  wood  to  it  so 
that  the  wood  projects  beyond  the  end  of  the  hose.  A 
better  plan  is,  to  insert  in  each  end  of  the  hose  a  tightly 
fitting  piece  of  lead  pipe,  which  is  coiled  once  round  in 
a  spiral  form.  The  hose  having  been  filled  with  water, 
is  laid  across  the  side  of  the  vat,  the  inner  end  dipping 
beneath  the  surface  of  the  liquid. 

Air  cannot  pass  the  curves  in  the  leaden  portion  of 
the  syphon  while  it  is  full  of  liquid,  so  that  if  the  work- 
man neglects  to  lower  it  as  the  liquid  in  the  vat  subsides, 
no  inconvenience  results,  and  the  flow  is  resumed  as 
soon  as  the  inner  end  is  lowered  by  drawing  the  hose 
over  the  side  of  the  vat. 


RECOVERY  OF  ABSORBED  GOLD. 

176.  The  false  bottoms,  of  perforated  wood,  and  the 
chlorinating  vats,  should  be  burned  when  no  longer  re- 
quired, as  they  contain  a  considerable  quantity  of  gold. 
At  my  works  at  Melrose  the  ashes  of  the  four  false 
bottoms  yielded  about  $90  worth  of  gold  and  silver. 
The  vats  were  assayed  by  boring  a  hole  in  one,  burn- 
ing the  chips  and  smelting  the  ashes,  which  gave  only 
$6  per  tub,  and,  as  they  were  still  serviceable,  it  would 
not  have  been  profitable  to  burn  them.  I  attribute  the 
fact  of  the  vats  having  absorbed  so  much  less  gold  than 
the  false  bottoms,  to  the  circumstance  that  they  had 
previously  been  used  in  the  Hunt,  Douglass,  and  Stew- 
art copper  silver  process,  and  were  quite  saturated 
with  brine,  etc.,  while  the  false  bottoms  were  of  new 
lumber.  Both  were  tarred. 


108  ADDENDA. 

GENERATORS. 

177.  There  are  several  forms  of  generator.  That 
described  differs  slightly  from  those  in  general  use.  In 
Deetken's  generator,  with  water  joint  cover,  the  wall 
of  the  water  chamber  is  not  high  enough  to  allow  of 
rilling  the  vessel  with  water,  to  expel  the  chlorine. 
Kustel  describes  one  in  which  the  stem  of  the  stirrer 
passes  through  a  stuffing  box  instead  of  a  water  joint, 
and  in  place  of  a  water  joint  for  the  main  cover,  is  a 
shallow  groove  containing  clay  and  a  little  water.  I 
have  used  this  joint,  and  it  answers  very  well,  but 
hardly  allows  of  filling  the  generator  with  water.  A 
stirrer  is  not  indispensable;  at  Crosby's  works  in  Ne- 
vada City  it  was  not  used. 

I  think  the  apparatus  shown  in  Plate  5  has  some 
advantages  over  the  others.  Generators  for  chlo- 
rine are  sometimes  made  like  a  "  carbonic  acid  i^s " 

o 

generator,  so  that  any  required  pressure  can  be  had, 
but  much  pressure  is  not  required  in  the  ordinary  way 
of  working  ores  with  chlorine. 


WASH-BOTTLES. 

178.  The  wash-bottle  described  (68)  is  of  my  own 
contrivance.  Kustel  describes  one,  made  from  an 
acid-carboy,  arranged  like  that  which  I  have  described 
for  the  working  test.  Deetken  used  simply  the  bell 
glass,  standing  in  an  open  basin  of  water,  with  leaden 
pipes  for  the  introduction  and  eduction  of  the  gas, 
passing  under  the  edge  of  the  bell.  This  arrangement 
would  seem  liable  to  upsetting.  I  used  one  in  which 


ADDENDA,  109 

the  bell  was  secured  vertically,  in  a  tub  of  water,  by 
means  of  a  cross  board  fixed  in  the  tub,  with  a  hole  to 
fit  the  bell.  The  gas  was  introduced  by  a  leaden  pipe, 
passing  under  the  bell,  and  escaped  through  the  neck 
of  the  latter,  with  which  a  rubber  pipe  was  connected. 

The  objection  to  a  bell  standing  in  an  open  vessel 
containing  water  is,  that  the  water  becomes  saturated 
with  chlorine,  which  is  constantly  evolved  from  the 
exposed  surface.  This,  though  not  important  in  a  well 
ventilated  room,  may  produce  inconvenience  in  closer 
quarters.  The  carboy  is  less  convenient  than  the  bar- 
rel for  the  renewal  of  the  water,  besides  being  liable  to 
accidental  breakage.  So,  on  the  whole,  I  think  that  my 
contrivance  is  to  be  preferred.  The  barrel  will  be  the 
better  for  being  tarred  inside;  better  still  if  coated  with 
paraffin. 

If  there  is  any  difficulty  in  finding  a  bottle  which  will 
admit  the  chlorine  pipe  through  the  neck,  it  will  answer 
to  pass  the  pipe  through  the  head  of  the  keg.  The 
gas  will  find  its  way  to  the  bell,  and,  if  the  keg  is  full 
of  water,  the  bubbling  of  the  chlorine  will  be  as  visible 
as  if  it  were  delivered  immediately  under  the  bell, 
which,  however,  must  be  set  higher  than  in  the  figure 
in  this  case,  unless  the  pipe  be  of  lead,  and  curved  so 
as  to  deliver  under  it. 

It  is  not  essential  that  the  gas  should  be  seen  to 
pass,  because  it  can  always  be  heard  bubbling  through 
the  water,  so  that  a  glass  bell  is  not  absolutely  re- 
quired, but  it  is  convenient,  enabling  one  to  see  that 
the  proper  quantity  of  water  is  in  the  keg. 

The  water  should  be  renewed  once  in  two  or  three 


110  ADDENDA. 

weeks,  and  that  which  is  drawn  out  can  be   utilized  in 
making  the  precipitant  for  gold  from  scrap  iron. 

SIFTING    ORE. 

179.  The   usual   method   of  sifting  the   damp  ore 
into  the  vats,  by  means  of  a  shaking  sieve  worked  by 
hand,  is  tedious.     The  roasted  ore  might  be  sifted  dry 
through  a  rotatory  cylinder  sieve,  by  hand  or  by  power, 
and  afterwards  moistened  as  usual;  then  thrown  lightly 
into  the  vat,  by  being  shaken   off  a   shovel,   and  dis- 
tributed by  raking.      This  method  would  admit  of  the 
use  of  a  fine  sieve. 

COST  OF  ACID. 

180.  Sulphuric  acid  of  60°  Beaum6,  or  1.76  sp.  gr., 
containing,  according  to  Ure,  69.31   per   cent  of  "  dry 
acid,"   costs  four   cents  per  pound  in   San    Francisco. 
One  pound  of  this  acid  is  equal  to  i  .06  pounds  of  acid 
of  63°  Beaume,  or   1.71   sp.  gr.,  containing  65.25  per 
cent  of  dry   acid,   and   costing  2*^   cents  per  pound. 
From  this  it   is   evident   that   the   weaker  acid   is   the 
cheaper  to  use,  unless  freight  costs  15  cents  per  pound. 
(Double  freight   is   charged   on   acid   by   the   Railroad 
Companies.)     For  example:— 

i  Ib.  of  acid  of  66° 4  cents. 

i  Ib.  freight 15 

19  cents. 

i. 06  Ibs.  of  acid  of  63°.  .  .    2.65  cents, 
i. 06  Ibs.  freight  at  15  cts.  .  15.9 

18-55    " 


ADDENDA.  Ill 

Taking  into  consideration  the  freight  on  the  carboys,' 
which  must  be  paid  both  ways  if  they  are  returned, 
though  not  equally,  an  addition  of  about  30  per  cent' 
must  be  made  to  the  weight  on  which  double  freight 
must  be  paid,  and  about  20  per  cent  of  ordinary  freight, 
or  10  per  cent  of  the  first  addition,  making  the  cost  of 
the  acids  respectively: 

Strong  acid  per  Ho.  as  above..  19.       cents. 

Freight  on  carboy  going 4.5        " 

"         "         "     returning. .  .  .0.45 

23.95  cents. 

Weak  acid  as  above,  i. 06  fbs.  ..18.55  cents. 

Freight  on  carboy  going 4.77      " 

"         "         "     returning. . ,   0.47 

—     23.79  cents. 

The  carboys  are  charged  for  at  the  rate  of  $2.25  each, 
and  if  not  returned  their  cost  must  be  added  to  that  of 
the  acid.  This  makes  an  inappreciable  difference  in 
the  relative  cost  of  the  two  grades.  Acid  can  be 
bought  and  freighted  more  cheaply  if  a  carload  is  taken 
at  once. 

SALT,  MANGANESE,    AND   ACID. 

181.  According  to  the  chemical  view  of  the  pro- 
duction  of  chlorine  from  salt  and  manganese,  under  the 
action  of  sulphuric  acid,  26.8  pounds  of  pure  salt  is  suffi- 
cient for  20  pounds  of  pure  manganese  binoxide.  But, 
in  this  connection,  two  points  must  be  considered. 
Firstly,  the  commercial  salt  and  manganese  are  never 
pure,  the  former  not  often  containing  more  than  90 
per  cent  of  sodium  chloride,  while  the  latter  is  consid- 


112  ADDENDA. 

ered  to  be  a  good  article  if  it  contains  70  per  cent 
binoxide.  Secondly,  the  theoretical  reaction  is  not  per- 
fectly realized  in  practice. 

If  the  proportion  of  salt  is  too  small,  as  compared 
with  that  of  the  manganese  and  acid  used,  the  latter 
two  will  react,  giving  off  oxygen,  and  forming  man- 
ganese sulphate,  so  that  the  subsequent  addition  of 
more  salt  will  not  repair  the  error.  A  mistake  in 
the  direction  of  an  excess  of  salt  can  be  rectified  by 
an  addition  of  acid  and  manganese,  but  as  salt  is  the 
cheapest  of  the  three  substances,  this  is  less  important. 
In  the  directions  given  (94)  for  making  chlorine,  the 
proportions  are  those  in  common  use,  and  the  salt  is 
intended  to  be  somewhat  in  excess  of  the  other 
substances. 

In  case  the  quality  of  the  salt  or  manganese 
should  differ  much  from  the  assumed  average,  there 
might  be  a  considerable  waste  of  one  or  the  other, 
whence  it  seems  desirable  that  the  reader  should  be 
informed  as  to  the  manner  in  which  these  substances 
may  be  assayed,  in  order  that  they  may  be  propor- 
tioned correctly. 

182.  Assay  of  Salt. — -Take  a  fair  sample  of  the  salt 
to  be  assayed.  It  must  not  be  dried,  because  what  is 
required  is  its  value  for  the  production  of  chlorine  in 
the  condition  in  which  it  is  to  be  weighed  for  working, 
but,  if  too  coarse,  it  should  be  crushed.  Mix  thor- 
oughly. Dissolve  ro  grains  in  about  50  grains,  or 
rather  less  than  y%  fluid-ounce,  of  distilled  or  rain  water, 
or  at  least  water  which  gives  no  precipitate  on  addition 
of  a  drop  of  solution  of  silver  in  nitric  acid.  Filter  the 
solution  through  a  small  wetted  filter  of  fine  bibulous 


ADDENDA.  1  13 

paper.  The  filter  must  be  well  washed  with  water  to 
completely  remove  the  salt  solution,  and  the  filtrate  and 
washings  received  in  a  flask. 

To  the  filtered  solution  in  the  flask  add,  drop  by 
drop,  a  solution  of  silver  nitrate  until  no  further  precip- 
itation of  silver  chloride  takes  place.  Warm  slightly, 
and  shake  vigorously,  stopping  the  mouth  of  the  flask 
with  a  greased  cork,  until  the  precipitate  is  found  to  set- 
tle readily,  leaving  the  liquid  clear.  Now  transfer  to  a 
small  filter,  the  weight  of  which  has  been  previously 
ascertained  after  drying  on  a  water  bath  until  it  no 
longer  lost  weight.  Wash  the  precipitate  and  the  filter 
with  hot  water  until  the  washings  are  tasteless.  Dry 
the  filter,  containing  the  precipitate,  on  a  water  bath 
until  two  successive  weighings  give  the  same  result. 
From  the  weight  obtained  deduct  that  of  the  filter ;  the 
remainder  Will  be  the  weight  of  silver  chloride  produced 
by  10  grains  of  the  salt. 

If  the  salt  were  pure  and  dry,  10  grains  would  pro- 
duce 24.53  grains  of  silver  chloride,  but  if  we  say  24.5 
grains"  it  will  be  sufficiently  accurate.  Multiply  the 
weight  of  silver  chloride  found  by  100,  and  divide  by 
24.5  ;  the  result  will  be  the  percentage  of  pure  salt  in 
the  sample.  EXAMPLE: — The  silver  chloride  obtained 
from  jo  grains  of  the  sample  weighs  net  19.3  grains; 
then  the  sample  contains  1930-4-24.5  =  78.77  per  cent 
of  pure  salt. 

The  silver  chloride  should  be  dried  without  much 
exposure  to  light.  For  a  water  bath,  the  cover  of  a 
vessel  in  which  some  water  is  boiling  answers  very 
well.  The  pulp  scales  used  in  assayh,  ore  are 
sufficiently  accurate  for  this  work,  if  sensitive  to 
iV  grain. 


114 


ADDENDA. 


183.  The  salt  sometimes  contains  a  considerable 
quantity  of  sodium  carbonate,  which  neutralizes  an 
equivalent  quantity  of  acid.  In  the  interior  of  the 
country,  where  this  is  most  liable  to  occur,  acid  is  very 
expensive  on  account  of  the  cost  of  freight.  Such  salt 
should  therefore  be  purified,  by  dissolving  it  in  water, 
and  exposing  the  solution  to  evaporation  in  shallow 
vats,  when  the  purified  salt  will  be  deposited. 

1.84.  Assay  of  Manganese. — Take  a  short  necked, 
flat  bottomed  flask  of  three  ounces  capacity,  and  fit 
into  it  a  cork  through  which  pass  two  glass  tubes  of 
about  y%  inch  bore.  One  of  the  tubes  must  extend 
nearly  to  the  bottom  of  the  flask ;  the  other,  about  three 
inches  in  length,  is  bent  to  a  right  angle  about  an  inch 
from  one  end,  the  shorter  limb  being  passed  through 
the  cork.  Now  take  the  barrel  of  a  small  glass  syringe, 
such  as  is  used  for  medical  purposes,  the  orifice  of 
which  must  be  enlarged  by  cutting  off  a  portion  of  the 
beak.  Fit  a  cork  to  the  larger  end,  and  through  it  pass 
the  disengaged  end  of  the  bent  tube,  the  other  end  of 
which  is  in  communication  with  the  flask.  Place 
in  the  syringe  some  pieces  of  pumice  stone,  and  moisten 

them  with  sulphu- 
ric acid;  attach  to 
the  bent  tube  by 
means  of  the  cork. 
A  test  tube  sus- 
pended from  the 
neck  of  the  flask 
completes  the  ap- 
paratus, which  is 
represented  by  the 
accompany  ingcut. 


ADDENDA.  115 

Weigh  99  grains  of  the  finely  pulverized  man- 
ganese which  place  in  the  flask.  Add  one  ounce  of 
cold  water,  and  then  150  to  160  grains  of  sulphuric 
acid.  Replace  the  cork  in  the  neck,  with  the  glass 
tubes,  and,  applying  the  lips  to  the  orifice  of  the 
syringe,  suck  air  through  the  flask.  This  is  done  for 
the  purpose  of  removing  any  gas  which  the  acid  may 
cause  to  be  evolved  from  impurities  in  the  manganese., 
Now  weigh  150  grains  of  oxalic  acid  which  place  in 
the  test  tube,  put  the  entire  arrangement  upon  the  pan 
of  a  balance  which  will  indicate  TV  grain,  and  counter- 
poise it. 

Remove  the  apparatus  from  the  balance,  throw  the 
oxalic  acid  from  the  test  tube  into  the  flask,  cork  in- 
stantly and  set  aside  for  a  short  time.  When  efferves- 
cence ceases,  warm  slightly,  which  will  renew  it,  and 
when  no  more  gas  is  evolved  draw  air  through  the 
flask  as  before.  Place  the  entire  apparatus  again  on 
the  scales.  It  will  be  found  to  be  lighter  than  before, 
and  the  number  of  grains  required  to  restore  the  equili- 
brium will  be  the  percentage  of  binoxide  in  the  sample. 

This  method,  while  not  rigidly  accurate,  is  sufficiently 
so  for  practical  purposes.  It  depends  on  the  circum- 
stance that  oxalic  acid,  in  presence  of  sulphuric  acid 
and  manganese  binoxide,  is  converted  into  water 
and  carbonic  acid  gas,  (carbon  dioxide).  The 
water  remains  in  the  apparatus.  The  gas  escapes 
through  the  tube  containing  pumice  imbued  with  sul- 
phuric acid,  which  retains  any  vapor  of  water  which 
might  otherwise  pass  off,  the  last  portion  of  the  gas 
being  drawn  out  by  the  mouth  as  directed.  Thus 
nothing  but  the  carbonic  gas  escapes,  and  as  99  grains 


116  ADDENDA. 

of  pure  binoxide  produce  almost  exactly  100  grains  of 
the  gas,  it  follows  that  the  weight  lost  corresponds  to 
the  percentage  of  binoxide  in  the  sample. 

185.  Having  assayed  the  salt  and  manganese,  the 
relative  proportion  in  which  they  should  be  used  re- 
mains to  be  considered.  It  has  already  been  intimated 
that  practice  does  not  conform  strictly  to  theory,  not 
because  the  theory  is  incorrect,  but  because  the  condi- 
tions attainable  in  working  do  not  admit  of  its  complete 
realization.  Hence  it  is  found  necessary  to  use  sul- 
phuric acid  in  excess  of  the  chemical  equivalent  of  the 
manganese,  and  as  sulphuric  acid  is  only  useful  in  con- 
junction with  a  sufficient  quantity  of  salt,  the  latter  must 
also  be  in  excess  of  the  manganese. 

For  this  reason,  instead  of  only  27  pounds  of  pure 
salt  to  20  pounds  of  manganese  binoxide,  we  use  36 
pounds  ;  these  quantities  usually  suffice  for  the  chlori- 
nation  of  three  tons  of  roasted  ore.  In  order  to  ascer- 
tain how  many  pounds  of  the  impure  materials  must 
be  used,  it  is  only  necessary  to  divide  the  quantity  of 
the  pure  substance  required  by  the  fraction  representing 
the  percentage  found  in  the  assay. 

Example:  Suppose  the  assay  of  the  salt  gave  87 
per  cent,  it  is  required  to  know  how  much  of  it  is  equal 
to  36  pounds  of  pure  salt,  then  36 -=-.8  7=4 1.3  7  pounds; 
again,  if  the  manganese  is  66^  per  cent,  then 
20-^.665=30  pounds  of  the  manganese  to  41  pounds  of 
the  salt,  which  is  about  the  proportion  generally  used, 
but  either  or  both  of  the  substances  may  vary  from  this 
supposition. 

As  to  the  acid,  the  quantity  required  depends  so  much 
on  the  temperature  of  the  generator,  and  the  nature  and 


ADDENDA.  117 

quantity  of  the  impurities  in  the  other  materials,  that 
no  other  rule  can  be  given  than  this;  it  must  be  added 
in  small  portions  as  long  as  it  continues  to  develope  a 
useful  quantity  of  chlorine.  It  will  soon  be  discovered 
how  much  is  required  for  a  given  quantity  of  salt  and 
manganese. 

The^  strength  of  the  acid  is  indicated  by  its  density, 
as  measured  by  a  Beaume  hydrometer,  which  is  simply  a 
floating  gauge — the  higher  it  floats  the  stronger  is  the 
acid,  and  the  reverse. 

SURPLUS  CHLORINE. 

186.  The  gasometer,  suggested  for  the  removal  of 
surplus  chlorine  (98),  might  be  made  by  attaching 
a  leaden  curtain  to  a  disc  of  wood  to  which  the 
suspending  chains  would  then  be  fastened.  A  light 
tub,  with  wooden  hoops,  thoroughly  soaked  with  paraf- 
fin or  ozokerite,  would  probably  answer  the  purpose. 

The  chlorine  withdrawn  from  the  vats,  would,  most 
likely,  be  contaminated  with  air,  and  as  its  re-use  is  not 
of  great  importance,  the  apparatus  might  be  simply  used 
to  blow  air  through  the  ore  mass,  from  below  the  filter, 
thus  expelling  the  chlorine  through  a  hose  connecting 
with  the  hole  in  the  cover  of  the  vat,  and  conducting 
out  of  the  room. 

In  this  way  there  would  be  no  difficulty  in  the  con- 
struction of  the  bell,  as  either  wood  or  iron  could  be 
used.  Other  methods  of  blowing  air  through  the  ore 
will  readily  suggest  themselves. 

Precipitating  vats  for  gold  are  sometimes  made  in 
the  form  of  rectangular  tanks  of  wood,  lined  with  sheet 


118  ADDENDA. 

lead.  This  vat,  though  more  expensive  than  a  wooden 
tub,  has  some  advantages.  There  is  no  risk  of  absorp- 
tion of  the  gold  solution,  and  it  is  not  necessary  to  add 
the  precipitant  until  the  vat  has  received  its  quota  of 
solution.  Then,  if  the  solution  contains  much  free 
chlorine,  a  jet  of  steam  may  be  introduced  and  the 
chlorine  driven  off,  after  which  the  precipitation ^of  the 
gold  by  means  of  iron  sulphate  proceeds  better,  and 
with  a  smaller  consumption  of  the  precipitant. 

As  it  is  necessary  to  heat  the  solution  in  order  to 
drive  off  the  chlorine  in  this  way,  it  cannot  be  thus  done 
so  thoroughly  in  a  tarred  tub,  on  account  of  the  softening 
of  the  tar.  It  could,  however,  be  done  by  blowing  air 
through  the  solution. 


PRECIPITATING   GOLD. 

187.  It  occurred  twice  in  my  works  that  on  collect- 
ing the  precipitated  gold  it  was  found  to  be  brick  red, 
instead  of  having  the  usual   brown  color.      It  was  also 
deficient  in  quantity.     On  the  first  occasion  I  could  not 
account  for  this,  but  on  the  second  I  satisfied  myself  that 
the  workman  had  not  thoroughly  mixed  the  precipitant 
with  the  solution,  and  being  consequently  deceived  by 
a  test,    he   had  not    used   iron   sulphate    in    sufficient 
quantity. 

188.  If  the  solution  of  gold  contains  lead  chloride, 
the  iron  sulphate  causes  a  precipitation  of  lead  sulphate, 
which  renders  the  subsequent  washing  of  the  gold  diffi- 
cult.    This  may  be  prevented  by  precipitating  the  lead 
as  sulphate  by  means  of  sulphuric  acid,  or  any  soluble 
sulphate  by  which  the  gold  will  not  be  affected,  as  so- 


ADDENDA.  119 

dium  sulphate.  After  settling,  the  liquid  must  be 
transferred  to  another  vat,  in  which  the  precipitation  of 
the  gold  is  effected  as  usual. 

In  some  cases  the  leach  contains  substances  the 
character  of  which  has  not  been  determined,  and  which 
affect  the  purity  of  the  precipitated  gold.  If  the  lixivium 
is  allowed  to  stand  several  hours,  a  deposit  is  formed  on 
the  sides  of  the  vat.  The  purified  solution  is  then 
drawn  off  into  another  vessel,  and  the  solution  of  iron 
sulphate  is  added. 

SUSPENDED    GOLD. 

189.  By  taking  some  of  the  waste  liquor  from  the 
gold  tub,  filtering   twice   through  Sweedish  paper,  and 
then  smelting  the  paper  with  litharge,  I  found  that  after 
24   hours  settling  there  remained  gold   in  suspension, 
equal  to  $1.00   in   value  for  each   ton   of  ore  leached. 
After  48  hours  I  still  found  half  that  quantity.     The  fil- 
trates from  these  tests  were  boiled  with    zinc   until  all 
precipitable  metals  were   thrown  down.     The  precipi- 
tate contained  no  gold,  which  shows  that  iron  perchlor- 
ide  does  not  dissolve  gold  in  presence  of  the  iron  proto- 
salts,  thus  setting  at   rest  a  doubt  which  had  arisen, 
as  to  whether  or  not  the  precipitated  gold  might  be,  to 
some  extent,  re-dissolved  by  remaining  for  many  hours 
in  contact  with  the   solution  of  iron  persalts,  which  is 
produced  when  gold  terchloride  is  decomposed  by  iron 
proto-sulphate. 

PRECIPITANTS  FOR  GOLD. 

190.  When  the   ore  contains  copper,  the  waste  so- 


120  ADDENDA. 

lution  from  the  tanks  in  which  the  copper  is  precipi- 
tated can  be  used  for  refilling  the  vat  containing  the 
precipitant  for  gold,  as  it  contains  a  large  quantity  of 
iron  protosalts,  chloride  and  sulphate.  The  strength 
must  be  reinforced  with  copperas,  or  acid  and  iron. 
The  waste  liquor  from  the  chlorine  generator,  consisting 
partly  of  manganese  proto-sulphate,is  also  a  good  precip- 
itant for  gold.  In  order  to  utilize  as  much  as  possible 
of  the  chlorine  which  it  contains,  as  well  as  any  free 
acid  which  may  be  present,  it  should  be  placed  in  a 
covered  tub,  or  small  vat,  with  some  scrap  iron. 
In  a  day  or  two  the  chlorine  and  the  acid  will  be  satur- 
ated with  iron,  thus  forming  an  additional  quantity  of 
precipitant. 

Other  preciptants  which  yield  the  gold  in  the  metal- 
lic state  are,  oxalic  acid,  sulphurous  acid,  the  antimony, 
arsenic,  and  copper  lower  chlorides,  and  animal  char- 
coal. The  latter  is  used  as  a  filter  on  which  the  gold 
solution  is  poured,  when  the  particles  of  carbon  become 
covered  with  a  film  of  gold.  It  is  patented.  In  some 
European  works  the  gold  is,  or  was,  thrown  down  as  a 
sulphide,  by  means  of  hydrogen  sulphide.  This 
method  has  the  disadvantage  of  precipitating  also 
copper,  and  some  other  metals,  if  present. 


SAND  IN    GOLD   MELTING. 

191.  Many  years  ago  I  was  employed  as  melter  in 
a  bullion  assaying  establishment,  and  was  often  called  on 
to  refine  gold,  which  was  done  by  granulating  and 
re-fusing  with  nitre  and  borax,  in  a  sand  pot.  It  often 


ADDENDY.  121 

happened  that  the  crucible  broke  in  the  furnace,  causing 
a  great  deal  of  trouble. 

Knowing  that  the  pots  were  attacked  not  only  by 
the  metal  oxides  produced  in  the  refining,  but  also  by 
the  potassa  resulting  from  the  decomposition  of  the 
nitre,  it  occurred  to  me  to  mix  some  clean  quartz  sand 
with  the  nitre,  which  answered  so  well  that  I  never 
afterwards  had  a  pot  broken  in  the  furnace. 


DRYING  CHAMBER. 

192.  For  drying  the  gold,  I  suggest  that  a  conve- 
nient arrangement  would  be  a  sheet-iron  closet,  in  the 
form  of  a  muffle,  in  the  dust  chamber,  with  a  door 
which  could  be  locked.  In  this  the  dishes  containing 
the  gold  could  be  left  with  safety  and  convenience  as 
long  as  necessary.  A  similar  but  larger  closet  could 
be  used  for  drying  the  silver  precipitate.  Such  a  closet 
is  represented  at  /,  Plate  7. 


VOLATILIZATION    OF    GOLD. 

193.  It  has  been  stated  by  some  authors  that  there 
is  never  much  loss"  of  gold  in  roasting  ores,  unless  the 
roasting  is  performed  too  rapidly,  and  that  the  addition 
of  salt  makes  no  difference  in  this  respect.  I  differ  with 
them  on  this  point,  even  when  the  statement  is  sup- 
ported by  so  formidable  a  name  as  that  of  Plattner. 
But  I  think  that  illustrious  chemist  would  yield  to  the 
logic  of  a  pecuniary  loss  of  three  thousand  dollars,  es- 
pecially when  backed  by  other  facts. 

When  I  first  entered  on  the  business  of  gold  chlori- 


122  ADDENDA. 

nation  on  the  large  scale,  I  had  a  class  of  concentra- 
tions to  treat  which,  while  consisting  chiefly  of  iron 
pyrites,  and  presenting  no  visible  peculiarity,  had  never- 
theless baffled  many  old  operators,  a  fact  of  which  I 
Was  not  at  the  time  aware.  The  ore  was  roasted  in  a 
three-hearth  reverberatory  furnace,  with  the  addition 
of  from  i  to  2  per  cent  of  salt,  on  account  of  the  pres- 
ence in  it  of  a  considerable  quantity  of  silver. 

I  was  surprised  to  find  that  although  .the  assays  of 
the  tailings  were  satisfactory,  the  gold,  when  collected; 
fell  alarmingly  short  of  the  results  which  I  had  guaran- 
teed, and  I  was  of  course  obliged  to  make  up  the  defi- 
cit. 

Relying  on  the  statement  referred  to,  which  I  found 
in  the  only  handbook  on  the  subject  within  my  reach, 
and  being  then  a  novice  in  this  branch  of  metallurgy,  I 
did  not  dream  that  a  serious  loss  was  taking  place  in  the 
roasting  furnace,  especially  as  I  had  an  expert  metal- 
lurgist in  reduced  circumstances  employed  on  the  roast- 
ing, who  had  no  more  suspicion  of  the  truth  than  I  had. 

Finding  that  I  was  sustaining  some  loss  by  inade- 
quate tub  room  for  the  gold  solution,  and  having  con- 
sequently to  draw  the  liquid  from  the  gold-tub  too  soon 
after  precipitation,  I  thought  that  I  should  find  the  whole 
loss  to  be  in  the  leaching  and  precipitating- department, 
and  each  time  that  an  improvement  was  made,  expected 
better  results,  so  that  I  was  led  on  from  trial  to  trial, 
until  the  total  loss  reached  the  sum  named. 

I  am  not  quite  certain  that  I  should  ever  have  dis- 
covered the  truth,  but  for  the  following  accident.  One 
day,  I  so  far  checked  the  draft  of  the  furnace  as  to 
cause  some  fumes  to  come  through  the  airholes  and 


ADDENDA.  123 

working  doors,  and  a  yellow  sublimate  on  the  masonry 
attracted  my  attention.  On  examination  I  found  the 
sublimate  to  be  very  rich  in  gold,  although  there  was 
none  to  be  seen  in  it  by  the  most  careful  washing.  It 
also  contained  iron  perchloride,  and  copper  chloride, 
with  some  lead  and  other  substances.  This  aroused 
my  suspicion,  and  I  at  once  did  what  I  ought  to  have 
done  sooner. 

Knowing  that  the  material  could  be  roasted  with  lit- 
tle or  no  loss,  if  no  salt  was  used,  because  some  assays 
had  been  made  in  that  way,  I  weighed  two  half  ounces 
of  a  sample,  and  roasted  them  in  the  muffle  side  by 
side,  under  precisely  the  same  conditions,  except  that 
to  one  of  them  I  added  4  per  cent  of  salt.  The  roast- 
ing was  purposely  pushed  to  an  extreme  as  to  heat  and 
time,  and  when  the  two  tests  were  assayed,  under  ex- 
actly similar  conditions,  that  which  was  salted  was 
found  to  contain  less  than  half  as  much  gold  as  the  un- 
saltecl  one. 

I  then  took  some  light  fluffy  sublimate  from 
the  flue  of  the  roasting  furnace,  an  assay  of 
which  gave  me  a  value  of  some  $600  per  ton, 
chiefly  gold.  The  quantity  of  this  material  was, 
however,  very  small,  and  the  bulk  of  the  matter  in 
the  dust  chamber  was  not  much  richer  than  the  aver- 
age of  the  ore  treated,  a  circumstance  which  indicates 
that  the  gold  was  actually  to  a  great  extent  volatilized 
in  some  not  easily  condensable  form.  I  also  found  that 
the  ore  sustained  a  loss  of  weight  in  roasting,  equal  to 
about  1 8  per  cent,  consequently  the  roasted  ore  ought 
to  have  been  more  than  18  per  cent  richer  than  before 
roasting,  which  was  not  the  case. 


124  ADDENDA. 

If  this  is  not  considered  to  be  sufficient  proof 
that  gold  may  be  volatilized  in  the  roasting  of 
some  ores  with  salt,  the  deficiency  is  supplied 
by  the  fact  that,  as  soon  as  I  made  the 
necessary  change  by  reserving  the  salt  until  the 
nearly  dead  roasting  of  the  ore  was  finished,  not  only 
did  the  roasted  ore  assay  20  per  cent  richer  than  when 
raw,  but  the  yield  overran  my  guarantee,  while  the 
tailings  nevertheless  contained  considerably  more  gold 
than  before. 

The  moral  of  this  is,  never  to  neglect  any  precaution 
in  the  way  of  tests  and  assays,  nor  to  place  implicit  reli- 
ance on  rules  laid  down,  or  inferences  drawn  by  others 
who  have  worked  under  different  conditions. 

I  afterwards  found  that  a  very  small  quantity  of  salt, 
not  more  than  three  pounds  to  the  ton,  might  be  mixed 
with  the  crude  ore  without  detriment  to  the  gold,  and 
with  decided  advantage  to  the  extraction  of  the  silver. 


SOLUTION  OF  SILVER  IN   HYPO. 

194.  The  statement  that  silver  chloride  dissolves  in 
a  solution  of  calcium  hyposulphite  is  not  strictly  accu- 
rate. It  is  decomposed,  exchanging  constituents  with 
the  calcium  salt,  forming  calcium  chloride  and  silver 
hyposulphite.  The  latter  combines  with  another  por- 
tion of  calcium  hyposulphite,  and  forms  a  double  salt, 
silver  calcium  hyposulphite,  which  is  very  soluble  in 
water. 

If  calcium  pentasulphide  is  added  to  such  a  solution 
in  equivalent  proportion,  one-fifth  of  its  sulphur  com- 


ADDENDA.  125 

bines  with  silver  to  form  silver  sulphide,  which  is  pre- 
cipitated, together  with  the  remaining  four-fifths  of  the 
sulphur,  The  oxygen,  and  so-called  hyposulphurous 
acid,  which  were  combined  with  the  silver,  combine 
with  the  calcium  of  the  decomposed  precipitant.  Thus 
the  portion  of  the  solvent  which  was  decomposed  by 
silver  chloride  is  reproduced. 

From  this  it  follows  that,  for  every  atom  of  silver 
extracted  from  the  ore,  and  precipitated  by  polysul- 
phide,  the  solvent  gains  a  molecule  of  calcium  chloride, 
without  however  having  ultimately  lost  any  hyposul- 
phite, and  this  is  the  reason  why  the  density  of  the  so- 
lution ceases  to  be  an  index  of  its  solvent  power.  So 
far  there  is  neither  a  loss  nor  a  gain  of  calcium  hypo- 
sulphite in  the  dissolving  solution,  but,  as  stated  else- 
where, the  precipitant  always  contains  a  quantity  of 
that  salt  in  watery  solution,  which  being  added  to  the 
solvent,  increases  its  volume  without  impairing  its 
strength,  unless  the  precipitant  is  too  much  diluted. 

In  practice  the  increase  or  diminution  in  strength  and 
volume  of  the  solvent  depends  on  the  care  exercised 
in  saving  as  much  of  it,  with  as  little  addition  of  wash 
water,  as  possible,  and  in  having  the  precipitant  suffi- 
ciently concentrated.  Kustel  gives  6°  Beaumd,  as  a 
minimum  density  for  the  latter. 


WASTE  OF  SULPHUR. 

195.  The  quantity  of  sulphur  required  for  the  pre- 
cipitation of  silver  is  really  only  as  16  to  108,  but  a 
great  waste  occurs  in  the  process  described,  from  two 
causes  :  Firstly,  there  is  always  a  certain  quantity  of 


126  ADDENDA. 

base  metal  dissolved  with  the  silver,  which  also  takes  its 
portion  of  sulphur  from  the  calcium  sulphide;  sec- 
ondly, a  large  proportion  of  the  sulphur  is  thrown  down 
in  a  free  state,  and,  in  the  usual  course  of  procedure,  is 
totally  wasted  by  being  burned  off  in  the  roasting  of  the 
precipitate. 

The  reason  for  this  precipitation  of  free  sulphur  is 
that  the  precipitant  is  necessarily  a  pentasulphide,  for 
the  calcium  mono  sulphide  is  insoluble,  and  the  bisul- 
phide is  only  soluble  with  heat  (vide  Regnault],  so  that 
for  our  purpose  we  are  restricted  to  the  pentasulphide. 

But  in  the  precipitation,  only  one-fifth  part  of  the  sul- 
phur of  the  pentasulphide  can  enter  into  combination 
with  the  silver,  forming  silver  sulphide,  and  as  the  cal- 
cium combines  with  the  oxygen  and  hyposulphurous 
acid  which  were  combined  with  the  silver,  the  remain- 
ing four-fifths  of  the  sulphur  are  unoccupied  and  use- 
less. 

Base  metals,  when  present  in  the  solution,  act  simi- 
larly, combining  with  only  a  portion  of  the  sulphur  of 
the  pentasulphide,  only  arsenic  and  antimony  forming 
pentasulphides.  Gold  forms  tersulphide,  but  its  quan- 
tity is  usually  insignificant  in  the  lixivium. 


RECOVERY  OF  SULPHUR. 

196.  There  are  two  methods  by  which  the  free  sul- 
phur may  be  recovered  from  the  precipitate.  The  first, 
introduced,  it  is  believed,  by  Ottokar  Hofman,  consists 
in  subjecting  the  mass  to  heat,  in  a  retort,  and  con- 
densing the  sublimed  sulphur.  The  second,  original 
with  myself,  and  which  seems  preferable,  is  as  follows  : 


ADDENDA.  127 

The  unwashed  precipitate  is  placed  in  a  vat  with  water, 
boiled  by  means  of  a  jet  of  steam,  and  slaked  lime  care- 
fully added. 

The  free  sulphur  combines  with  the  lime,  in  the 
manner  already  described,  producing  at  once  the  pre- 
cipitating solution  of  calcium  polysulphide,  and  much 
more  quickly  than  when  the  fresh  sulphur  is  used.  The 
boiling  can  be  done  in  a  filter  vat,  and  when  finished 
the  clear  solution  can  be  drawn  off.  The  precipitate  is 
washed  by  passing  hot  water  through  it,  dried  and 
roasted  as  usual.  Three-fourths  or  more  of  the  sul- 
phur is  thus  recovered  for  re-use. 


MATTE  FROM  THE  SILVER. 

197.  The  matte  obtained  in  melting  the  silver  pre- 
cipitate is  usually  quite  rich,  and  it  seems  to  be  impos- 
sible to  completely  desilver  it  by  means  of  iron  alone, 
at  least  in  the  presence  of  copper.  The  bullion  is  about 
.800  fine,  even  when  there  is  a  good  deal  of  copper  in 
the  precipitate,  because  very  little  copper  is  reduced 
from  the  sulphide  by  iron  at  a  white  heat.  It  is,  however, 
necessary  that  enough  sulphur  be  left,  in  the  roasting,  to 
convert  the  copper  into  sulphide,  for  if  too  much  oxide 
.is  formed  a  part  of  it  may  be  reduced  by  the  blacklead 
pot,  metallic  iron,  or  by  charcoal  if  present,  and  thus 
contaminate  the  silver.  Antimony  and  arsenic,  though 
their  sulphides  are  reduced  by  iron,  yet  volatilize,  or 
combine  with  a  further  portion  of  iron  and  remain  in 
the  matte.  Lead,  if  present  in  the  precipitate,  cannot 
be  kept  out  of  the  bullion.  Gold,  when  melted  in  the 
presence  of  sulphur  and  iron,  forms  a  black,  brittle  mass, 


128  ADDENDA. 

containing  much  iron,  but  the  gold  sulphide  obtained 
with  the  silver  precipitate  is  mostly  Deduced  in  the 
.melting,  and  the  metal  is  found  alloyed  with  the  silver. 

MELTING    FURNACE. 

198.  I  have  seen,  in  the  mining  regions,  many  bar- 
barously constructed  melting  furnaces,  some  of  which 
were  very  inconvenient  to  work  with.  A  description 
of  the  furnace  which  I  build  for  silver  melting,  where 
economy  is  an  object,  and  of  which  Figures  i  and  2, 
Plate  8,  are  sections,  will  probably  be  useful. 

This  furnace  is  suitable  for  a  number  30  or  35  black 
lead  pot,  with  charcoal  as  fuel.  There  is  no  heavy 
and  expensive  cast-iron  plate  on  the  top,  and  the  cover 
may  be  of  sheet-iron,  although  cast-iron  is  better. 

The  interior  may  be  cylindrical,  but  is  better,  as 
shown  in  the  figures,  narrowed  toward  the  top  and  bot- 
tom. The  grate  bars  rest  on  an  iron  ring,  Figure  3, 
supported  by  an  offset  in  the  masonry.  The  latter  is 
mostly  of  a  very  rough  kind,  as  the  furnace  is  sunk  in 
the  ground  to  within  a  foot  of  the  top,  which,  besides 
affording  great  convenience  in  working,  obviates  the 
necessity  of  iron  bands  or  stay-rods  to  support  it  against 
the  expansion  caused  by  the  heat.  The  greater  part 
of  the  lining,  4  inches  thick,  is  of  good  clay,  very  slightly 
moistened,  and  beaten  round  a  hollow  wooden  core,  for 
which  part  of  a  barrel  of  suitable  size  answers  very 
well.  It  is  topped  with  a  course  of  common  brick, 
and  above  these  is  a  flat  iron  ring,  Figure  4, 
with  lugs,  which  may  be  bolted  down,  or  simply  let  in 
flush  with  the  top  of  the  furnace. 


Plate  VRI. 


ADDENDA.  129 

The  grate  bars  are  not  built  in,  but  are  free  to  be 
removed  whenever  desired.  The  furnace  is  con- 
structed, when  convenient,  at  the  base  of  the  main 
smoke  stack,  with  which  it  is  connected  by  a  flue; 
otherwise  a  large  stove-pipe  will  answer  for  a  chimney. 
When  the  weight  of  melted  metal  does  not  exceed 
100  pounds  avoirdupois,  the  pot  is  lifted  out  of  the  fur- 
nace by  hand,  by  means  of  the  basket  tongs,  the  mould 
being  placed  on  the  platform  of  masonry  which  is  seen 
in  the  figure  on  one  side  of,  and  level  with  the  fur- 
nace. The  melter  stands  on  the  top  of  the  furnace  to 
lift,  then  steps  to  the  ground  one  foot  lower,  to  pour. 

If  larger  quantities  of  metal  are  melted  at  once,  a 
lever  may  be  employed  for  lifting  the  pot.  The  lever 
is  arranged  like  that  of  a  blacksmith's  bellows,  being 
supported  by  a  rope,  chain,  or  swivel,  in  such  a  man- 
ner as  to  admit  of  a  lateral  as  well  as  a  vertical  move- 
ment, and  at  a  height  of  not  less  than  six  feet  above  the 
furnace,  the  center  of  which  is  directly  under  the 
shorter  arm. 

From  the  longer  arm  of  the  lever  a  rope  depends; 
from  the  shorter  arm  a  link  of  half-inch  iron,  long 
enough  to  reach,  when  drawn  downward,  into  the 
cavity  of  the  furnace,  and  terminating  in  a  hook  engag- 
ing in  an  eyebolt  which  forms  the  pivot  connecting  the 
jaws  of  the  tongs. 

The  tongs  being  adjusted  on  the  pot,  a  ring  is  slip- 
ped over  the  handles  to  hold  them  together;  the  melter 
steadies  them,  while  an  assistant,  pulling  on  the  rope  at 
the  other  end  of  the  lever,  lifts  the  pot  out  of  the  fur- 
nace, and  swings  it  near  to  the  mould,  when  the  melter 
pours  the  metal. 


130  ADDENDA. 

The  hands  and  arms  of  the  melter  are.  protected  by 
gloves,  which,  in  some  works,  are  elaborately  made  of 
canvas  and  padding.  To  make  a  glove,  I  simply  take 
an  ore  sack,  double  it  lengthwise,  and  sew  it  so  as  to 
form  a  narrow  bag,  of  two  thicknesses  of  canvas,  into 
which  the  arm  may  be  thrust  to  the  shoulder.  The 
gloves  may  be  wetted  to  prevent  burning,  but  hot  arti- 
cles must  not  be  grasped  with  a  wet  glove,  because  the 
steam  produced  will  scald  the  hand;  yet,  moisture  is  a 
good  protection  against  radiant  heat,  while  grasping 
the  cool  handles  of  the  tongs. 

In  melting  with  charcoal,  the  best  result  is  obtained, 
not  by  keeping  the  furnace  full,  but  by  letting  nearly 
all  the  fuel  burn  away,  before  refilling.  A  little  prac- 
tice will  enable  the  melter  so  to  manage  that  there 
shall  be  but  little  coal  in  the  furnace  when  the  time  for 
pouring  arrives,  so  that  it  is  not  in  the  way  when  seiz- 
ing the  pot  with  the  basket  tongs.  The  lifting  must  be 
performed  without  delay,  otherwise  the  tongs  may  be- 
come red  hot,  and  bend.  The  feet  and  legs  of  the 
melter  may  be  protected  by  woolen  armor,  or  by  wet- 
ting the  boots  and  trowsers ;  but  melters  and  assayers 
must  not  shrink  from  a  little  scorching. 

If  there  is  much  fuel  left  in  the  furnace  when  the 
melting  is  ended,  the  grate  is  taken  out,  and  the  em- 
bers fall  into  the  ash  pit,  where  they  are  extinguished. 

Clinkers,  if  formed  on  the  sides  of  the  furnace,  from 
the  melting  of  the  lining,  or  from  dirty  fuel,  are  punched 
off,  while  red  hot,  by  means  of  an  iron  bar  with  a  chisel 
end.  If  they  were  to  be  removed  after  cooling,  the 
walls  would  be  broken. 

If  making  a  bar  of  clean  skimmed  metal,  it  is  proper 


ADDENDA.  131 

to  throw  a  little  resin,  or  powdered  charcoal  into  the 
pot,  a  few  seconds  before  pouring.  It  prevents  the 
sputtering  which  is  often  caused  by  the  formation  of 
base  oxides.  As  soon  as  such  a  bar  is  cast,  the  top  of 
it  is  covered  with  charcoal  powder,  to  prevent  oxida- 
tion while  solidifying  When  the  slag  or  matte  is 
poured  with  the  metal  the  charcoal  is  not  required. 

The  addition  of  sand  in  melting  an  impure  precipi- 
tate, especially  when,  by  over-roasting,  a  good  deal  of 
base  metal  sulphate  or  oxide  has  been  formed,  is  very 
beneficial  in  saving  the  pot,  by  slagging  the  oxides  by 
which  it  would  otherwise  be  attacked. 

Charcoal  is  used  to  effect  the  deoxidation  of  sulphates, 
which  would  otherwise  take  place  at  the  expense  of  the 
plumbago  pot.  It  is  also  employed  to  prevent  the 
formation  of  a  crust,  or  to  reduce  the  same  if  formed, 
on  the  surface  of  the  matte. 


SODIUM   HYPOSULPHITE. 

199.  Sodium  hyposulphite  may  be  made  by  passing 
sulphurous  acid  (sulphurous  anhydride)  and  air  through 
a  solution  of  sodium  sulphide,  produced  by  fusing  to- 
gether five  parts  of  sodium  sulphate  (a  common  product 
of  the  marshes  in  the  interior)  and  one  part  of  pulver- 
ized charcoal,  and  extracting  with  water. 

The  sodium  polysulphide  may  also  be  used.  It  is  made 
by  boiling  a  solution  of  caustic  soda  on  excess  of  sulphur, 
or  by  fusing  together  sodium  carbonate  and  (sulphur, 
and  dissolving  in  water.  Caustic  potassa  (concentrated 
lye)  may  be  used  in  place  of  caustic  soda,  making  potas- 
sium polysulphide,  and  then  .  potassium  hyposulphite 


132  ADDENDA. 

with  sulphurous  acid  and  air.  The  potassium  salt 
answers  the  same  purpose  as  that  of  sodium. 

Sodium  hyposulphite  may  also  be  made  by  heating 
a  solution  of  sodium  sulphite  with  sulphur.  The  latter 
is  dissolved.  The  sulphite  is  made  by  passing  sulphur- 
ous acid  through  a  solution  of  sodium  carbonate,  or  by 
exposing  the  latter,  in  a  moist  condition,  to  the  fumes 
of  burning  sulphur  (sulphurous  anhydride)  in  a  rever- 
beratory  furnace,  or  in  the  flue  of  a  roasting  furnace. 

For  all  the  purposes  mentioned,  the  sodium  carbon- 
ate or  bicarbonate  may  be  used  indifferently. 

It  has  been  asserted,  by  some  writers,  that  the  solu- 
tion of  sodium  hyposulphite  does  not  dissolve  any  gold, 
even  in  those  cases  in  which  the  calcium  salt  does  so, 
referring  to  that  lower  gold  chloride  which  sometimes 
exists  in  ore  which  has  been  roasted  with  salt  (30). 
This  however  is  a  mistake,  as  has  been  proved  by 
direct  experiment,  more  than  half  of  the  contained  gold 
having  been  extracted  from  a  sample  of  such  ore,  by 
leaching  it  with  the  solution  in  question. 


THE  CHLORINATION  ASSAY. 

200.  The  so-called  chlorination  assay,  is  so  far  in- 
correct that  it  gives  not  only  the  silver  chloride, 
but  all  other  silver  compounds  which  are  soluble  in  so- 
lutions of  the  alkaline  or  earthy  hyposulphites  It  may 
seem  that  this  is  a  matter  of  indifference,  since  all  the 
silver  that  can  thus  be  extracted  can  be  obtained  in  the 
large  operation,  and  this  view  is  correct  as  to  the  silver 
sulphate. 


ADDENDA.  133 

But,  in  roasting  silver  ores,  if  all  the  requisites  of  a 
thorough  chloridation  are  not  present,  certain  compounds 
of  silver  are  forme;!,  which,  though  soluble  in  hypo  (or 
in  hot  brine),  and  therefore  extracted  in  the  ordinary 
chlorination  assay,  are  neither  chloride  nor  simple  sul- 
phate. These  compounds  render  the  extraction  of  the 
silver  more  difficult,  and  affect  the  purity  of  the  result- 
ing bullion,  whether  the  leaching  process,  or  amalga- 
mation be  employed. 

As  ammonia  dissolves  the  chloride  and  sulphate,  but 
not  the  compounds  alluded  to,  I  suggest  that  compara- 
tive assays  be  made,  occasionally,  with  hypo  and  with 
ammonia,  as  the  solvents. 

The  following  account  of  some  investigations,  made 
in  1876,  and  published  at  the  time  in  the  Mining  and 
Scientific  Press,  will  assist  in  explaining  this  matter: 

i. — Roasted  ore  containing  silver,  per  ton $65.00 

A.  Leached  with  ammonia,  retained  per  ton.  .13.20 

B.  Leached  with  solution  of  sodium  hyposul- 
phite, retained  per  ton 5.20 

2. — Roasted  ore  containing,  per  ton 60.00 

A.  Leached  with  ammonia  (after  digestion  for 
several  hours  in  warm  ammonia),  retained 

per  ton 15.00 

B.  Leached   with    sodium    hyposulphite,   re- 
tained per  ton 3.50 

3. — Sample  of  amalgamation  tailings   containing 

silver,  per   ton 9.00 

A.  Washed  on  filter  with  cold  water;  filtrate 
contained  a  chloride,  but  gave  no  precipi- 
tate with  solution  of  potassium  sulphide. 


134  ADDENDA. 

B.  Rewashed  with    hot  water ;    filtrate   con- 
tained neither  chlorine  nor  heavy  metal. 

C.  Again  washed,  with  cold  solution  of  sodium 

hyposulphite;  filtrate  tested  with  potassium 
sulphide  gave  a  copious  brown  precipitate 
containing  silver,  lead,  arsenic,  iron,  etc. 

D.  Excess  of  potassium   sulphide  was  added 
to  filtrate  (7,  and  afterwards,  to  prevent 
re-solution  of  arsenic,  iron  protosulphate  in 
slight  excess,  then  nitric  acid  to  decom- 
pose the  hyposulphites.     A  white  precipi- 
tate was  slowly  formed,  which  on  boiling 
became  yellow  (sulphur). 

E. — Precipitate  from  D,  removed  by  filtration, 
and  filtrate  treated  with  an  acid  solution 
of  silver  nitrate,  gave  no  precipitate. 

The  inference  is,  that  the  metal  salts  contained  in 
the  washed  tailings,  and  dissolved  by  solution  of  so- 
dium hyposulphite,  were  not  chlorides. 

4. — Sample  of  amalgamation  tailings   contain- 
ing silver,  per  ton $4.00 

A.  Washed  on  filter  with  hot  water;  filtrate 
tested    with    barium   nitrate    showed  the 
presence  of  a  sulphate.     Washing  contin- 
ued   until    no    more    sulphate   could    be 
detected. 

B.  Washing  repeated  with  hot  solution  of  so- 
dium chloride  (free  from  sulphate) ;  a  por- 
tion of  the  filtrate  tested  with  potassium 
sulphide,  gave  a  copious  pecipitate;    the 


ADDENDA.  135 

remainder  tested  with  barium  nitrate  also 
gave  an  abundant  precipitate. 

The  inference  is  that  the  metal  salts  extracted  by 
sodium  chloride  were  sulphates,  and  as  the  silver  is  ex- 
tracted by  hot  brine  about  as  perfectly  as  by  sodium 
hyposulphite,  it  seems  probable  that  the  metals 
exist  as  a  multiple  sulphate,  otherwise  the  silver  sul- 
phate would  have  been  extracted  by  hot  water  alone. 
The  tailings  gave  no  appreciable  silver  chloride  by 
treatment  with  ammonia.  The  metals  extracted  by 
hot  brine  are  very  slowly  reduced  by  metallic  iron,  so 
that  a  good  result  is  obtained  from  ore  in  this  state,  in 
pans,  only  by  long  continued  working,  and  a  base  bul- 
lion is  obtained,  while  the  addition  of  lime  to  the  pulp, 
intended  to  produce  finer  bullion,  entirely  prevents  the 
reduction,  causing  richer  tailings.  With  silver  chlo- 
ride, even  a  great  excess  of  lime  does  not  impede 
reduction,  nor  prevent  amalgamation,  though  the  latter 
is  somewhat  impeded.  By  longer  roasting  of  the  ore, 
the  formation  of  silver  chloride  was  improved,  but 
the  ore  required  an  addition  of  sulphur,  in  some  form, 
to  give  the  best  attainable  result. 


CHLORINATION  TAILINGS. 

201.  However  carefully  the  ore  may  be  treated, 
a  certain  portion  of  gold  remains  in  the  tailings, 
varying,  other  things  being  equal,  according  to  the 
character  of  the  ore.  In  case  this  results,  in  part,  from 
the  presence  of  particles  too  large  to  be  entirely  dis- 
solved, that  portion  can  be  extracted  by  re-treatment, 


or 


y 


136  ADDENDA. 

either  with  gas,  by  chlorine  water,  or  by  amalgamation. 
But  a  portion,  which  is  sometimes  quite  considerable, 
still  remains,  and  resists  every  mode  of  chlorination  or 
amalgamation,  and  can  only  be  extracted  by  smelting 
with  lead. 

In  general,  it  may  be  said  that  gold  which  can  be 
seen  by  the  aid  of  a  lens,  after  finely  grinding,  and  care- 
fully washing,  a  sample  of  the  tailings,  can  be  extracted 
by  chlorination,  or  amalgamation;  but  that  which  can- 
not thus  be  rendered  visible  can  neither  be  chlorinated 
nor  amalgamated,  even  if  the  ore  be  re-roasted,  with  or 
without  re-grinding.  (If  re-ground  it  forms  a  pasty 
mass,  which  cannot  be  leached,  being  almost  impervi- 
ous to  water.)  Of  course  the  ore  is  supposed  to  be 
properly  roasted  in  the  first  instance. 

Concentrated  sulphides  containing  gold,  and  free 
from  lead,  will  frequently  yield  as  much  as  98  per  cent 
of  the  fire  assay,  if  moderately  rich,  but  the  extraction 
of  95  per  cent  is  considered  a  good  result,  from  ore 
containing  $100  worth  of  gold  in  a  ton.  As  the  mate- 
rial loses  about  24  per  cent  of  its  weight  in  the  roasting 
and  leaching,  it  will  readily  be  perceived  that,  if  there 
has  been  no  sensible  loss  of  gold  in  the  roasting,  the 
tailings  from  such  ore  will  assay  about  $6  per  ton,  and 
for  every  hundred  tons  of  ore  treated  there  will  be  76 
tons  of  tailings,  containing  $456  worth  of  gold. 

Tailings  of  this  character,  consisting  chiefly  of  iron 
peroxide,  make  an  excellent  flux  for  the  smelting  of 
galena.  All  the  precious  metal  they  contain  is  ex- 
tracted, together  with  the  lead  set  free  from  the  galena 
by  the  action  of  the  iron  oxide,  and  may  be  considered 
as  clear  profit  to  the  smelter,  who  is  obliged  to  use 


ADDENDA.  137 

some  kind  of  iron  flux,  and  can  find  nothing,  unless  it 
be  metallic  iron,  better  adapted  to  his  purpose  than 
these  tailings.  Chlorination  tailings  can  also  be  util- 
ized in  the  manufacture  of  red  paint. 


VALUE  OF  BARS. 

202.  Large  bullion  scales,  and  troy  weights,  are  not 
always  at  hand;  yet  it  is  often  desirable  to  know  the 
value  of  a  bar  before  sending  it  away  from  the  works, 
and  as  good  counter  scales,  with  advoirdupois  weights, 
are  generally  accessible,  the  following  facts  may  be 
found  useful. 

The  assay  value  of  one  advoirdupois  pound  of  pure 
silver  is  $18.85;  tnat  of  one  advoirdupois  ounce  is  $1.17 
The  pound  of  pure  gold  is  worth  $301.44,  and  the  ounce 
$18.84.  Hence  it  is  easy  to  calculate  the  value  of  a 
bar  of  which  the  fineness  is  known,  and  which  has  been 
weighed  on  common  counter  scales  to  the  nearest  quar- 
ter ounce.  For  example:  a  silver  bar  is  .969  fine,  and 
weighs  82  Ibs  3*4  ounces. 

Then:  $18.85  x.969  =  $i8.26x  82  $1,497.82 

and  1.  17  x.  969=       i.i3x    3/i  =  3-67 


Making  the  value  of  the  bar  $1,500.99 

Each  1(Joth  of  silver  in  a  bar  is  worth  1.885  cents? 
and  each  ^ih  of  gold  30.14  cents  per  advoirdupois 
pound;  therefore,  if  in  the  above  example  the  bar  con- 
tained also  a  little  gold,  say  .003,  and  perfect  accuracy 
is  not  required,  it  would  be  sufficient  to  add  to  the 
value  3  times  30.14  cents  for  each  pound  weight,  or  in 
all  $74.14.  Again,  a  gold  bar  is  .969  fine  and  weighs 


138  ADDENDA. 

7  Ibs.  13^02.,  or  125^02.;  then  18.84  x  .969=18.26  x 
i25^=$2,29i.63.     Or,  the  value  of  a  gold  bar  may 
be  calculated  as  though   it  were  silver,  and   the  result 
multiplied  by  16. 

The  commercial  or  market  value  is  different  from  the 
assay  value.  The  discount  on  silver  varies  from  lo.to 
15  per  cent  of  the  assay  value,  to  which  is  added  one- 
half  of  one  per  cent  for  mintage,  or  assayer's  fee. 
Gold  bars  free  from  base  metal  are  subject  to  a  dis- 
count or  a  premium,  equal  to  one-tenth  of  one  per  cent 
for  every  ten  "  points,"  or  thousandths,  above  or  be- 
low the  quoted  par  fineness;  discount  if  above,  premium 
if  below.  The  apparent  anomaly  is  due  to  the  fact 
that,  if  there  is  no  base  metal  in  the  bar,  all  that  is  not 
gold  is  silver,  whence  at  par  fineness,  there  is  just 
enough  of  silver  in  the  bar  to  pay  parting  charges,  etc., 
while  in  a  finer  bar  those  charges  must  be  met  by  a 
discount  on  the  value  of  the  gold.  Conversely,  a  bar 
which  is  below  par  fineness  commands  a  premium  for 
the  extra  silver  it  contains.  On  account  of  this  arrange- 
ment, bars  which  are  more  than  half  gold,  are  stamped 
with  the  gold  value  only,  unless  they  contain  much  base 
metal,  when  both  gold  and  silver  value  is  stamped  on 
them. 

Mixed  bars  in  which  the  gold  forms  a  large  part  of 
the  value,  but  less  than  half  the  weight,  are  called 
"dore"  bars,  and  are  stamped  with  the  value  of  both  the 
gold  and  the  silver. 


CHLORINE. 

203.     Chlorine  plays  such  an  important  part  in  con- 
nection with  human  industry,  that  a  short  sketch  of  its 


ADDENDA. 


history  and  properties  cannot  but  be  interesting  and 
useful. 

Chlorine  is  an  elementary  body,  as  far  as  is  yet 
known.  It  is  true  that  this  substance  has  been  sus- 
pected by  chemists  to  be  a  compound,  but  although  its 
decomposition  has  been  more  than  once  announced,  it 
has  not,  within  the  writer's  knowledge,  been  verified. 

Chlorine  was  discovered  by  Scheele  in  1774,  and,  in 
accordance  with  the  crude  notions  then  entertained, 
was  called  "  dephlogisticated  marine  air."  Sir  Hum- 
phrey Davy  investigated  its  properties  at  a  later  date, 
and  gave  it  the  name  which  it  now  bears,  derived  from 
a  Greek  word  signifying  pale  green,  or  yellowish  green. 
The  name  of  the  mineral  "chlorite"  has  the  same  de- 
rivation, but  this  substance  contains  no  chlorine,  and 
must  not  be  conjfeunded  with  the  chlorous  acid  salts, 
which  are  also  called  chlorites. 

Under  ordinary  circumstances,  chlorine  is  a  pungent 
and  suffocating  gas  of  a  yellowish  green  color,  and  is 
2.44  times  as  heavy  as  an  equal  volume  of  air.  When 
compressed  to  one-fifth  of  its  normal  volume  it  becomes 
liquid,  and  is  then  1.33  times  as  heavy  as  an  equal 
volume  of  water. 

Chlorine  has  powerful  affinities,  which  cause  it  to 
combine,  under  suitable  conditions,  with  almost  every 
other  known  element.  When  naturally  combined  with 
silver,  it  forms  the  well  known  mineral  horn  silver.  It 
is  also  found  in  nature,  combined  with  lead,  copper,  and 
other  metals,  especially  with  sodium  in  the  compound 
known  as  common  salt.  When  it  is  considered  that 
the  entire  ocean,  covering  three-fourths  of  the  surface 


140  ADDENDA. 

of  the  globe,  with  a  depth,  in  places,  of  several  miles, 
is  heavily  charged  with  salt,  and  that  over  six-tenths  of 
the  weight  of  salt  consists  of  chorine,  it  will  be  per- 
ceived that  a  more  definite  statement  could  hardly  qon- 
vey  a  more  definite  idea  of  the  enormous  quantity  of 
chlorine  existing  in  the  world.  If  all  the  chlorine  in 
the  ocean  could  be  set  free  at  once,  it  would  destroy 
every  vestige  of  life  on  the  globe. 

In  combination  with  hydrogen,  chlorine  forms  hydro- 
chloric acid  gas,  and  in  this  form  is  evolved  in  enor- 
mous quantities  in  the  manufacture  of  soda-ash  from 
salt,  by  the  agency  of  sulphuric  acid.  The  gas,  dis- 
solved in  water,  forms  ordinary  hydrochloric  or  muri- 
atic acid.  This  acid,  in  contact  with  manganese  binox- 
ide,  evolves  chlorine,  and  it  is  in  this  way  that  chlorine  is 
produced,  in  countries  where  the  acid  is  a  waste  pro- 
duct of  the  soda  works,  for  the  manufacture  of  the 
so-called  chloride  of  lime,  or  bleaching  powder.  In 
this  country  the  use  of  chlorine  is  limited,  and  we  gen- 
erally make  the  hydrochloric  acid,  and  develop  chlorine 
from  it  at  the  same  time,  by  means  of  a  mixture  of  salt, 
manganese  binoxide,  and  dilute  sulphuric  acid,  as  ex- 
plained in  the  directions  for  the  chlorination  of  gold 
ores.  The  best  remedy  for  the  effects  of  an  accidental 
inhalation  of  chlorine  is,  to  breathe  the  vapor  of  water 
or  alcohol,  or  to  drink  a  glass  of  spirits. 


PLATTNER'S  PROCESS. 

204.      The    process    of  gold    extraction    known  as 
Plattner's  chlorination  process,  which  is  that  described 


ADDDENA.  141 

in  the  text,  originated  in  Europe,  and  was  first  intro- 
duced here  by  G.  F.  Deetken,  M.  E.,  at  Grass  Valley, 
in  Nevada  County. 

In  1866,  Mr.  Deetken  having  removed  from  Grass 
Valley,  the  operators  who  succeeded  him  were  suddenly 
confronted  by  a  difficulty  in  the  treatment  of  the  con- 
centrations from  the  Eureka  mine,  which  all  at  once 
developed  an  amazing  capacity  for  absorbing  chlorine, 
so  that  the  application  of  Plattner's  process  to  them 
was  no  longer  profitable.  The  writer,  happening  to 
visit  Grass  Valley  in  that  year,  was  applied  to  for  a 
remedy  for  the  difficulty,  which,  not  being  aware  of  the 
cause,  nor  having  facilities  for  investigation,  he  was  not 
able  to  supply ;  but  the  matter  being  made  public 
through  the  medium  of  the  Mining  and  Scientific  Press, 
it  arrested  the  attention  of  Mr.  Deetken,  who  at  once 
repaired  to  the  spot,  and,  with  his  well  known  skill,  and 
professional  sagacity,  detected  the  cause  of  the  diffi- 
culty and  applied  the  remedy. 

The  trouble  was  occasioned  by  the  presence  of  a 
rnagnesian  compound  in  the  concentrated  sulphurets. 
By  the  addition  of  a  small  quantity  of  salt  to  the  roast- 
ing mass,  this  substance  was  converted  into  magnesium 
chloride  in  the  furnace,  much  more  cheaply  than  it 
could  be  done  by  means  of  chlorine  in  the  vats.  The 
gold  was  then  chloridized  in  the  usual  manner.  The 
use  of  salt  in  the  furnace  for  this  purpose  was,  so  far  as 
is  known  to  the  writer,  original  with  Mr.  Deetken,  being 
quite  distinct  from  its  use  for  the  purpose  of  chlori- 
dizing  silver,  when  present  in  the  ore.  To  this  gentle- 
man we  also  owe  the  demonstration  of  the  possibility  of 
conducting  the  process  in  wooden  vessels. 


142  ADDENDA. 

THE   KISS    PROCESS. 

205.  The  use  of  alkaline  or  earthy  hyposulphites 
for  the  extraction  of  silver  from  ores,  also  originated  in 
Europe,  having  been  suggested  by  Dr.  Percy,  in  1848, 
and  first  applied  in  practice  by  Von  Patera,  in  1858,  at 
Joachimsthal.  Von  Patera  used  the  sodium  hyposulphite 
for  the  leaching,  and  the  sodium  polysulphide  for  the 
precipitation.  This  method  was  modified  by  Kiss,  who 
substituted  the  calcium  salts  for  those  of  sodium. 

The  Kiss  process  was  first  successfully  introduced 
on  this  coast  by  Kustel  and  Hofman,  in  Mexico,  after 
abortive  attempts  had  been  made  by  others  in  Lower 
California.  It  met  with  such  success  as  to  supercede 
amalgamation  in  the  treatment  of  silver  ores,  through- 
out the  State  of  Sonora,  and  the  Territory  of  Lower 
California,  and  was  even  known  among  ill  informed 
people  as  the  "  Mexican  process."  It  has  been  gradu- 
ally growing  in  public  favor,  the  principal  obstacle  to 
its  extensive  adoption  in  the  silver  regions  of  Nevada 
being  the  circumstance  that  the  ores  of  that  State 
usually  carry  more  or  less  gold,  which,  while  frequently 
not  justifying  the  application  of  the  Plattner  process,  is 
but  partially,  and  almost  by  chance,  extracted  in  the 
Kiss  silver  process. 

One  great  objection  to  the  use  of  the  Plattner  process 
in  these  cases  is,  the  cost  of  acid,  the  transportation  of 
which  is  troublesome  and  expensive.  It  is  therefore 
desirable  that  some  means  of  developing  pure  chlorine 
from  salt  cheaply,  without  the  use  of  acid,  should  be 
devised. 


ADDENDA.  143 

THE  BRUCKNER  FURNACE. 

206.  This  furnace  consists  of  a  horizontal,  brick- 
lined,  hollow  cylinder,  of  boiler  iron,  with  central  open- 
ings at  the  ends,  through  which  the  flames  from  a  fixed 
fireplace  pass  to  a  flue  connecting  with  a  dust  chamber, 
while  thq  cylinder  rotates  slowly  on  rollers.  The  ore 
is  introduced  and  discharged,  periodically,  by  means  of 
trap  doors  in  the  side  of  the  cylinder.  The  latter  is 
divided  lengthwise  by  a  reticulated,  spiral  partition,  or 
diaphragm,  composed  of  cast-iron  plates  supported  by 
hollow  cast-iron  bars,  which,  passing  through  the  walls 
of  the  cylinder,  admit  of  a  circulation  of  air  through 
them,  with  the  design  of  protecting  them  from  too  great 
heat. 

The  function  of  the  diaphragm  is  twofold;  firstly,  to 
lift  the  ore,  and  shower  it  through  the  heated  air  within 
the  furnace  as  the  latter  revolves;  secondly,  to  move 
the  ore  from  end  to  end  of  the  cylinder,  in  order  that 
all  portions  of  the  ore  may  be  equally  exposed  to  heat. 

The  diaphragm  is  liable  to  rapid  destruction  by  the 
action  of  sulphur,  arsenic,  and  antimony  in  the  ore.  It 
is  stated,  on  excellent  authority,  that  the  loss  of  the 
diaphragm  does  not  impair  the  efficiency  of  the  furnace, 
In  some  cases  the  furnace  has  been  found  to  work  bet- 
ter without  the  diaphragm,  forming  fewer  lumps  in  the 
roasting  of  leady  ores. 

In  this,  as  in  all  rotating  cylinder  furnaces,  the  light 
and  fine  portion  of  the  ore  is  carried  away  by  the  force 
of  the  draft.  It  is  therefore  necessary  that  extensive 
dust  chambers  be  provided,  through  which  the  draft 
from  the  furnace  must  pass,  on  its  way  to  the  chimney, 


144  ADDENDA. 

in  order  that  the  principal  part  of  the  dust  may  be  de- 
posited. 

The  writer  superintended  the  erection  and  working 
of  one  of  these  furnaces  in  Inyo  County,  and  obtained 
satisfactory  results  from  it.  About  15  per  cent  of  the 
ore  passed  to  the  dust  chamber,  and  was  found  to  be  but 
imperfectly  roasted.  This  dust  was  collected,  slightly 
moistened  with  a  solution  of  salt  and  iron  sulphate  in 
water,  and  then  returned  to  the  furnace,  and  success- 
fully roasted.  About  the  same  percentage  of  it  again 
found  its  way  to  the  dust  chamber. 

The  cylinder  is  twelve  feet  long  by  six  feet  in  diame- 
ter, and  a  charge  for  it  is  from  \y2  to  2^/2  tons  of 
ore,  with  the  necessary  salt.  The  time  required  for 
the  roasting  of  a  charge  of  ore  in  this  furnace  is  from 
four  to  twelve  hours,  including  the  charging  and  dis- 
charging. 

As  the  weight  of  the  charge  varies  with  the  quality 
of  the  ore,  and  the  degree  of  fineness  to  which  it  is 
•crushed,  and  the  time  required  for  the  roasting  varies  with 
the  same  circumstances,  the  capacity  of  the  furnace  may 
be  said  to  range  from  four  to  twelve  tons  in  24  hours. 
One  man  on  a  shift  can  do  all  the  work,  or  can  attend 
to  the  firing  of  four  furnaces. 

This  furnace  has  been  extensively  used  in  treating 
the  silver  ores  of  Colorado  and  Mexico,  and  one,  with- 
out the  diaphragm,  is  now,  or  was  recently  employed  in 
the  roasting  of  auriferous  sulphurets  in  Nevada  County, 
California. 


ADDENDA.  145 

THE    BRUNTON   FURNACE. 

207.  This  furnace  is  essentially  similar  to  the 
Bruckner,  but  has  no  diaphragm.  In  form  it  differs 
slightly,  being  ovoid,  or  egg  shaped,  the  larger  end 
toward  the  fire.  This  form  must  conduce  to  the  stability 
of  the  brick  lining,  and  is  said  to  roast  the  ore  more: 
evenly  than  the  cylinder.  The  rotation  of  the  furnace- 
is  not  produced,  as  in  the  Bruckner,  by  means  of  a 
pinion  engaging  in  a  toothed  rack  surrounding  the  shell, 
but  simply  by  the  traction  of  the  rollers,  two  of  which 
are  connected  by  a  strong  shaft,  to  which  motion  is. 
imparted  by  means  of  a  screw  on  a  transverse  shaft. 
This,  with  the  absence  of  the  diaphragm,  a  low  royalty 
for  the  patent  right,  and  some  other  peculiarities,  ren- 
der the  furnace  cheaper  than  the  Bruckner.  A  Brun- 
ton  furnace  twelve  feet  long  by  six  feet  eight  inches, 
in  its  greatest  diameter,  recently  constructed  for  the 
chlorination  works  at  the  Plumas  National  Mine,  in 
Plumas  County,  California,  weighed,  including  gearing 
and  iron  bed-plates  for  the  rollers,  in  place  of  the  wooden 
ones  formerly  used,  nearly  10  tons  without  the  lining 
bricks. 


THE   PACIFIC  CHLORIDIZING    FURNACE. 

208.  This  is  a  simple  brick  lined  rotating  cylinder,, 
not  differing  essentially  from  those  described.  It  is. 
however  made  of  large  capacity,  as  much  as  seven  tons, 
of  ore  being  treated  at  once.  A  good  feature  in  the 
make-up  of  this  furnace  is  that  the  charging  hoppers,. 


146  ADDENDA. 

of  which   there  are   two,  are   supplied   by  the  foundry 
already  mounted  on  iron  supports. 


THE  WHITE  FURNACE. 

209.  The  White  furnace  consists  of  a  hollow  rotatory 
brick-lined  cylinder  of  cast-iron,  with  open  ends.  The 
brick  lining  is  so  arranged,  in  the  short  segments  of 
which  the  cylinder  is  composed,  as  to  form  "grooves, 
cavities  or  projections,"  by  which  the  ore  is  lifted  and 
showered  through  the  flames,  which  pass  through  the 
furnace  from  end  to  end.  The  cylinder  is  slightly  in- 
clined, either  downward  from  the  fireplace,  or  the  re- 
verse, and  the  pulverized  ore  is  poured  automatically  and 
continuously,  together  with  the  salt,  into  the  higher 
end.  The  rotation,  aided  by  the  lifting  and  dropping 
of  the  ore,  causes  the  latter  to  traverse  the  entire  length 
of  the  cylinder,  and  to  fall  continuously  from  the  lower 
end.  By  an  ingenious  arrangement,  the  inclination  of 
the  cylinder  is  rendered  adjustable,  so  that  the  ore  may 
occupy  a  longer  or  a  shorter  time  in  passing  through  it. 

When  the  furnace  is  so  arranged  that  the  cylinder  is 
inclined  upward  from  the  fireplace,  and  the  ore  conse- 
quently enters  at  the  cooler  end,  it  results  that  the 
lighter  dust  does  not  pass  through  the  furnace,  but  is 
carried  by  the  force  of  the  draft  in  the  opposite  direc- 
tion, toward  the  flue,  and  into  a  series  of  chambers  in 
which  the  greater  part  of  it  settles,  while  the  smoke, 
etc.,  passes  on  to  the  chimney.  To  effect  theroasting  of 
this  portion  of  the  ore,  an  auxiliary  fire  is  necessary, 
through  the  flames  of  which  the  dust  may  pass  on  its 


ADDENDA.  147 

way  to  the  chambers.  The  coarser  portion  of  the  ore 
•passes  along  the  cylinder,  under  continually  increasing 
heat,  and,  on  its  exit  at  the  lower  end,  falls  into  a  pit, 
situated  between  the  end  of  the  cylinder  and  the  main 
fireplace,  where  it  is  exposed  to  the  heat  of  the  flames 
passing  over  it.  At  stated  periods,  the  accumulated  ore 
is  removed  from  the  pit  and  spread  on  the  cooling  floor. 
This  arrangement  of  the  cylinder — the  ore  entering 
at  the  cooler  end — fulfils,  better  than  the  reverse  plan, 
the  requisite  conditions  of  a  proper  roasting.  The 
writer  is  not  aware  of  an  instance  in  which  the  inclina- 
tion was  downward  from  the  fireplace,  and  the  ore  en- 
tered the  furnace  at  the  hotter  end,  in  which  satisfac- 
tory results  were  obtained. 


THE  HOWELL-WHITE  FURNACE. 

210.  The  furnace  known  by  the  above  appellation, 
is  a  modification  of  the  White.  The  cylinder  is  lined 
with  bricks  in  only  one-third  of  its  length  from  the  lower 
•end,  adjoining  the  fireplace,  the  diameter  of  this  por- 
tion of  the  iron  shell  being  10  inches  greater  than  that 
of  the  unlined  portion 

The  ore  enters  the  cylinder  at  the  upper  and  cooler 
end,  and  is  lifted  and  showered  by  means  of  projections 
which  in  the  unlined  portion  are  formed  of  iron,  in  the 
lined  portion  of  projecting  bricks. 

The  inclination  of  the  cylinder  is  fixed,  the  time  oc- 
cupied by  the  ore  in  passing  through  it  being  regulated 
by  the  number  of  rotations  per  minute,  which  is  adjust- 
.able  at  will. 


148  ADDENDA. 

The  length  of  the  cylinder  is  23  feet  2  inches.  The 
internal  diameter  of  the  smaller  part  of  the  iron  shell  is 
from  22  to  50  inches,  that  of  the  enlarged  portion  being 
as  stated  10  inches  more,  in  order  to  admit  of  lining. 

The  working  capacity  of  the  furnace  ranges  from  eight 
to  forty-five  tons  of  ore  in  24  hours,  according  to  the 
character  of  the  ore  and  the  diameter  of  the  cylinder. 


THE  THOMPSON-WHITE  FURNACE. 

Another  modification  of  the  White  furnace  has  been 
made  by  J.  M.  Thompson. 

This  furnace  differs  from  the  Howell-White  in  sev- 
eral particulars.  The  cylinder  is  of  one  diameter 
throughout  its  length,  and  is  lined  throughout  with 
tiles,  thus  lessening  the  loss  of  heat  by  radiation,  which 
must  be  considerable  in  the  unlined  portion  of  the 
Howell-White  furnace.  The  tiles  are  specially  molded 
for  the  purpose,  and  are  so  formed  that  the  projections 
and  recesses,  designed  to  lift  the  ore,  are  of  a  rounded 
form  as  to  their  transverse  section.  In  some  cases  the 
recesses  are  obstructed  at  intervals  by  transverse 
ridges.  The  intention  of  this  is  to  prevent  the  ore 
sliding  along  in  the  inclined  cylinder,  in  consequence  of 
its  low  angle  of  stability  at  an  early  stage  of  the  roasting. 
In  some  ores  this  angle  becomes  almost  nil,  so  that  the 
powder  resembles  a  fluid  in  its  action. 

The  further  retention  and  equalization  of  heat  in  the 
cylinder,  is  promoted  by  means  of  a  layer  of  non-con- 
ducting material,  such  as  paris  plaster,  or  asbestos,  be- 
tween the  lining,  of  bricks  or  tiles,  and  the  iron  shell. 


o 

w 

o 

X 
o 


ADDENDA.  149 

The  latter,  and  the  supporting  rollers  with  their  bear- 
ings, are  thus,  in  a  measure,  protected  from  the  injuri- 
ous effects  of  unequal  or  excessive  heat,  by  being  kept 
comparatively  cool. 

The  furnace  is  arranged  in  either  of  two  ways.  In 
the  one,  the  whole  of  the  ore  enters  the  cylinder  at  the 
higher  and  cooler  end.  In  this  case  the  lighter  dusty 
portion  which  is  carried  back  by  the  draft,  is  roasted 
by  the  flames  from  an  auxiliary  fire  between  the  end 
of  the  cylinder  and  the  dust  chambers,  the  latter  being 
constructed  of  masonry.  In  the  other,  the  dust  is  sep- 
arated from  the  coarser  portion  of  the  ore  before  enter- 
ing the  cylinder.  The  coarse  portion  then  enters  at 
the  upper  end,  while  the  dust  enters  at  the  lower  end 
near  the  fire.  The  main  fire  is  thus  made  to  serve  for 
the  roasting  of  both  portions  of  the  ore,  and  the  auxil- 
iary fire  is  dispensed  with.  It  is  also  claimed  by  the 
inventor,  with  considerable  show  of  reason,  that  the 
heat  and  the  chlorine,  developed  by  the  roasting  of  the 
dust,  mingled  as  it  is  with  salt,  instead  of  being  lost,  as 
when  an  auxiliary  fire  is  relied  on,  aids  materially  in 
chloridizing  the  coarser  portion  of  the  ore. 

A  portion  of  the  dust,  impelled  by  the  draft,  traverses 
the  entire  length  of  the  cylinder,  and  entering  the  flue 
is  arrested  in  its  flight  by  the  ordinary  means  of  dust 
chambers,  which,  in  this  case,  are  constructed  of  iron 
instead  of  masonry;  hence  they  are  light,  portable,  and 
cheap. 

The  length  of  time  occupied  by  the  passage  of  the 
coarser  portion  of  the  ore  though  the  cylinder,  is  regu- 
lated mainly  by  the  inclination  of  the  latter,  which,  as 
in  the  White  furnace,  is  adjustable,  though,  as  the  writer 


150  ADDENDA. 

is  informed,  in  a  different  manner.  Mr.  Thompson  pre- 
fers to  regulate  the  period  of  transit  by  varying  the  angle 
of  inclination,  rather  than  the  speed  of  rotation,  of 
the  cylinder,  arguing  that,  as  it  is  stated  by  eminent  met- 
allurgists that  the  loss  of  silver  by  volatilization  is,  other 
things  being  equal,  proportioned  to  the  length  of  time  dur- 
ing which  the  ore  is  exposed  to  the  heat,  it  follows  that 
the  more  quickly  the  ore  is  roasted  the  less  loss  it  will 
sustain.  But,  he  continues,  the  greater  or  less  rapidity 
of  the  roasting  depends  on  the  greater  or  less  exposure 
of  the  particles  of  ore  to,  first  oxidizing,  then  chloridiz- 
ing  influences,  or  to  both  simultaneously;  hence  the 
more  continuously  the  ore  is  showered  through  the 
heated  air  and  gases  pervading  the  interior  of  the  fur- 
nace, the  more  quickly  will  the  roasting  be  effected, 
and  consequently  less  loss  will  be  caused  by  the  volatil- 
ization of  silver. 

This  theory  seems  plausible.  Let  us  examine  it. 
Let  us  suppose  two  furnaces  in  operation,  receiving 
equal  quantities  of  the  same  kind  of  ore.  They  are 
alike  in  every  respect,  rotating  with  equal  speed,  fired 
in  the  same  manner,  and  with  the  same  amount  of 
draft.  They  will  yield  like  results. 

We  will  now  suppose  that  both  of  the  cylinders  are 
rotating  at  the  highest  feasible  rate  of  speed,  thus  af- 
fording the  greatest  exposure  of  the  ore  to  the  roasting 
influences.  It  is  desired  to  modify  their  action  so  that 
the  time  occupied  by  the  passage  of  the  ore  through 
them  may  be  doubled. 

In  one,  which  we  will  call  the  Howell,  this  result  is 
attained  by  reducing  the  speed  of  rotation.  (Owing  to 
the  effect  of  tangential  force  the  reduction  of  speed  will 


ADDENDA.  151 

be  somewhat  less  than  half.)  In  the  other,  or  Thomp- 
son, by  lessening  the  angle  of  inclination.  The  supply 
of  ore  to  each  is  supposed  to  remain  unchanged  for  the 
present.  An  analysis  of  the  effects  of  these  alterations 
gives  the  following  results. 

The  quantity  of  ore  passed  through  each  furnace  in 
a  given  time  remains  unaltered. 

The  quantity  of  fuel  and  air  consumed  by  each  is 
unchanged. 

The  quantity  of  ore  exposed  to  the  heat  at  any  given 
moment  in  each  is  doubled;  therefore,  the  time  during 
which  the  ore  is  exposed  to  heat  in  each  is  doubled. 

The  length  of  time  during  which  the  ore  is  drop- 
ping through  the  air  is,  in  the  Howell,  unchanged; 
in  the  Thompson,  doubled. 

The  power  consumed  in  lifting  the  ore  is — in  the 
Howell  unchanged  ;  in  the  Thompson,  doubled. 

In  the  Howell  the  same  quantity  of  work  is  performed, 
on  the  same  quantity  of  ore,  with  the  same  expenditure 
of  power,  as  before  the  change.  In  the  Thompson  a 
double  quantity  of  work  is  performed  on  the  same  quan- 
tity of  ore,  by  a  double  expenditure  of  power.  If  the 
ore  is  as  well  roasted  in  the  one  furnace  as  in  the  other, 
the  advantage  is,  so  far,  with  the  Howell.  Is  it  proba- 
ble that  the  same  result  can  be  produced  by  the  Howell 
as  by  the  Thompson,  with  half  the  work,  and  therefore 
half  the  power  ?  As  the  result  sought  is  a  chemical  one, 
the  answer  to  this  question  depends  on  the  extent  to 
which  the  attainment  of  that  result  is  accelerated  by  the 
movement  of  the  ore. 

The  time  occupied  by  the  oxidation  of  a  single  parti- 
cle of  sulphuret,  exposed  to  heated  air,  other  things 


152  ADDENDA. 

being  equal,  is  in  some  ratio  to  its  mass.  It  matters 
not  whether  an  adjacent  particle  consists  of  sulphuret 
or  quartz ;  the  two  particles  of  sulphuret  will  be  oxi- 
dized simultaneously,  in  the  same  length  of  time  as 
would  one  particle,  provided  the  requisite  quantity  of 
heated  oxygen  be  supplied.  As  regards  the  heat,  the  two 
particles  will  aid  each  other  by  their  combustion,  ren- 
dering necessary  a  smaller  proportionate  quantity  of 
fuel  than  if  one  particle  were  sulphuret,  and  the  other 
quartz. 

In  a  roasting  cylinder  there  is,  at  any  given  moment, 
a  certain  quantity  of  air,  capable  of  oxidizing  a  certain 
number  of  particles  of  sulphuret.  To  expose  a  greater 
number  of  particles  would  be  useless.  To  expend 
power  for  that  purpose  would  be  to  waste  the  power. 

If  we  suppose  the  quantity  of  oxygen  passing  through 
each  furnace  to  be  in  excess  of  the  quantity  which  can 
be  utilized,  the  feed  may  be  increased  in  both.  When 
the  quantity  of  air  passing  through  the  furnaces  is  in 
equilibrium  with  the  ore,  so  that  the  oxygen  is  utilized 
to  the  utmost  practicable  extent,  one  of  two  things  must 
be  true.  Either  the  Thompson  is  wasting  power  in 
lifting  the  ore  more  often  than  the  Ho  well,  or,  the  ore 
is  remaining  in  it  a  longer  time  than  is  necessary.  If 
the  former,  the  rate  of  rotation  should  be  reduced;  if 
the  latter,  the  inclination  of  the  cylinder  should  be  in- 
creased. The  latter  is  the  most  probable,  because, 
although  it  is  not  denied  that  oxidation  proceeds  to  a 
certain  extent  while  the  ore  lies  quiescent  in  the  cylin- 
der, it  is  proved,  by  all  experience,  to  proceed  faster 
when  the  ore  is  showered  through  the  heated  air, 
provided,  as  before  said,  that  a  sufficient  quantity  of 


ERRATUM — Page  153,  third  line,  for  "  speed,"  read,  inclination. 


ADDENDA.  153 

free  oxygen  is  present,  which,  on  our  hypothesis,  is  the 
case  in  this  instance. 

If  the  speed  of  the  Thompson  is  now  increased,  the 
same  quantity  of  ore  will  pass  through  it,  but  the  time 
occupied  in  the  passage  will  be  lessened,  and  the  load 
in  the  furnace  will  be  reduced.  Less  power  will  now 
be  consumed  in  causing  the  cylinder  to  rotate,  and  the 
loss  of  silver  by  volatilization  will  be  diminished. 

Whether  the  power  required  would  be  reduced  to  an 
equality  with  that  consumed  by  the  Howell,  which 
would  mean  that  the  load  in  the  furnace  should  be  re- 
duced to  half  that  in  the  Howell,  or,  in  other  words  the 
time  of  passage  should  be  half,  or  whether  the  result 
would  be  a  mean  in  which  the  diminution  of  volatiliza- 
tion would  compensate,  or  more  than  compensate  for 
the  greater  consumption  of  power,  is  a  question  which 
can  only  be  answered  by  experiment. 

A  similar  view  as  to  the  chloridation,  which,  in  this 
class  of  furnace,  is  more  or  less  effected  by  the  falling 
of  the  ore  particles  through  the  heated  gases  evolved  by 
the  roasting  ore  and  the  salt,  would  lead  to  similar  con- 
clusions. But  the  theory  of  the  chloridation  is  opposed 
to  any  greater  movement  of  the  ore  in  this  stage  than 
is  necessary  to  ensure  equal  and  thorough  heating. 
Hence  it  would  perhaps  be  advantageous  to  have  a 
smaller  number  of  lifters  in  the  circumference  of  the 
cylinder  near  its  lower  or  chloridizing  end,  than  in  the 
central  and  upper  zones.  But  it  is  known  that,  in  this 
class  of  furnace,  a  considerable  percentage  of  the  chlo- 
ridation takes  place  after  the  ore  has  left  the  cylinder, 
and  while  it  is  accumulating  in  the  pit  into  which  the 


154  ADDENDA. 

cylinder  empties  itself.       Exactly  how  far  this  principle 
may  be  carried  in  practice  has  not  been  proved. 

The  objection  that  rapid  rotation  of  the  cylinder 
causes  the  separation  of  a  larger  quantity  of  dust  from 
the  roasting  ore,  is  too  puerile  to  be  worth  refuting. 
The  only  result  is  that  the  auxiliary  fire  has  more  to  do, 
and  the  cylinder  less,  a  clear  saving  of  motive  power,  or 
an  increase  in  the  capacity  of  the  furnace.  One  point 
in  this  connection  is  worthy  of  notice;  the  dusting 
almost  ceases  as  soon  as  the  ore  begins  to  " sponge." 
This  is  in  favor  of  feeding  the  dust  into  the  lower  end 
of  the  cylinder. 

Another  valuable  feature  in  the  Thompson  furnace, 
and  which  has  been  heretofore  surprisingly  overlooked 
by  inventors,  is  that  the  heat  given  off  by  the  roasted 
ore,  instead  of  being  wasted,  is  utilized  in  heating  the 
air  with  which  the  furnace  is  supplied ;  at  the  same  time 
the  ore  is  cooled  sufficiently  to  allow  of  its  being  moist- 
ened without  loss  or  inconvenience  from  the  formation 
of  a  great  volume  of  steam. 

Thompson  also  adapts  the  length  of  the  cylinder  in 
such  proportion  to  its  diameter,  and  to  the  extent  of 
grate  surface  in  the  fireplace,  as  that  the  heat  at  the 
higher  end  shall  be,  as  nearly  as  practicable,  that  which 
is  proper  for  the  initial  stage  of  the  roasting.  It  is  a 
self-evident  proposition  that  a  large  quantity  of  burning 
fuel  will  heat  a  cylinder,  not  only  of  greater  diameter, 
but  of  greater  length,  than  a  smaller  quantity.  Hence, 
if  the  length  of  the  cylinder  is  not  increased  in  suitable 
proportion  to  the  increased  diameter,  one  of  two  things 
must  happen:  either  the  larger  cylinder,  by  being  too 
short,  must  waste  available  heat  at  its  upper  end,  or, 


ADDDENA.  155 

the  smaller  cylinder,  being  too  long,  is  not  sufficiently 
heated  throughout.  As  the  proper  initial  heat  varies 
for  different  ores,  the  most  advantageous  length  of 
cylinder  for  a  given  diameter  will  also  vary.  The  usual 
dimensions  are  21,  24,  27,  and  30  feet  in  length,  to  32, 
40,  52,  and  60  inches  in  diameter,  respectively. 

As  to  the  question  of  the  best  manner  of  regulating 
the  operation  of  a  roasting  furnace  of  this  class,  the 
writer's  opinion  is,  that  the  cylinder  should  be  adjustable 
both  as  to  speed  of  rotation  and  as  to  inclination,  in 
order  that  it  may  be  adapted  to  the  various  require- 
ments of  different  ores.  In  the  White,  and  in  Thomp 
son's  modification,  this  is  the  case. 

The  roasting  of  ores  is  a  problem  in  which  mechani- 
cal and  chemical  factors  are  inextricably  interwoven. 
While  it  is  well  that  theory  should  suggest  and  guide 
experiment,  yet,  if  the  facts  thus  developed  oppose  the 
theory,  the  latter,  not  the  former,  must  give  way. 


THE    O'HARA    FURNACE. 

212.  This  is  a  reverberatory  furnace  of  great  length, 
the  hearth  being  about  one  hundred- feet  long  by  five  to 
^eight  feet  wide.  It  is  traversed  lengthwise  by  plows 
and  scrapers  attached  to  endless  chains,  which,  passing 
•over  rollers  at  the  ends  of  the  furnace,  carry  the  plows 
back  to  the  place  of  entrance,  where  the  ore  is  fed  in 
•continuously  by  a  mechanical  arrangement.  By  the  ac- 
tion of  the  plows  the  ore  is  not  only  turned  over,  but  is 
also  progressed  gradually  towards  the  hottest  part  of 
the  furnace,  thence  to  a  cooling  hearth,  and  is  finally 


156  ADDENDA. 

discharged  into  a  suitable  receptacle.  In  a  furnace  of 
this  size  several  fires  are  used  on  each  side,  at  different 
points  in  the  length.  A  great  advantage  of  this  furnace 
is,  that  very  little  of  the  ore  is  carried  to  the  flues  by  the 
draft.  It  can  be  operated  by  one  man  on  a  shift,  and 
has  a  capacity  of  as  much  as  40  tons  per  24  hours.  By 
a  recent  improvement  the  furnace  is  built  in  two  stories. 


STETEFELDT    FURNACE. 

213.  If  any  metallurgist  had  been  told,  prior  to  the 
introduction  of  the  Stetefeldt  furnace,  that  a  chlorid- 
izing  roasting  of  silver  ore  could  be  effected  in  the  short 
space  of  a  few  seconds  of  time,  he  would  probably  have 
been  incredulous.  In  the  old  reverberatory,  the  opera- 
tion requires  several  hours;  in  the  cylinder  furnaces  of 
continuous  action  it  occupies  from  10  to  30  minutes, 
but  in  the  furnace  now  under  consideration,  the  ore,  if 
not  of  extremely  refractory  character,  is  almost  com- 
pletely roasted  while  falling  from  a  height  of  little  more 
than  20  feet. 

The  furnace  consists  of  a  stack  or  shaft  of  masonry, 
provided  with  fireplaces  opening  into  it  near  the  base, 
with  a  flue  near  its  upper  end,  and  with  an  apparatus 
for  sifting  the  ore  and  salt  into  it  at  the  top.  The  ore 
thus  showered  from  the  top  of  the  stack,  encounters  in 
its  descent,  under  the  most  favorable  conditions  for 
chemical  action,  the  ascending  flames  and  heated  air 
from  the  fireplaces,  as  well  as  the  fumes  of  its  own 
combustion,  and  from  the  voltalization  and  decomposi- 
tion of  the  salt.  When  it  reaches  the  bottom,  where  a 


ADDENDA.  157 

hopper  is  provided  for  its  reception,  not  only  is  the  ox- 
idation completed,  but  the  chloridation  of  the  silver  is 
so  far  advanced  as  to  require  for  its  completion  only 
the  further  exposure  to  heat  which  the  ore  receives 
while  accumulating  in  the  hopper.  The  latter  is  emp- 
tied from  time  to  time,  by  means  of  a  slide,  into  iron 
cars  and  the  ore  removed  to  the  cooling  floor. 

As  in  all  other  processes  in  which  the  pulverized 
ore  is  showered  through  the  flames,  the  lighter  portion, 
amounting  sometimes  to  30  per  cent  of  the  whole,  is 
carried  back  by  the  current  of  air  and  gas.  In  order 
to  prevent  an  accumulation  of  dust  in  the  flue,  the 
latter  joins  the  stack  at  an  acute  angle,  and  is  con- 
ducted almost  vertically  downward  to  the  base,  where 
the  flames  from  an  auxiliary  fireplace  enter  it,  and 
effect  the  roasting  of  the.  dust,  which  then,  passing  into 
a  horizontal  flue,  settles  mainly  in  a  series  of  hoppers, 
while  the  hot  air,  smoke  and  gases  pass  through  dust 
chambers  to  the  chimney.  The  construction  of  the 
furnace  involves  many  ingenious  contrivances  for  regu- 
lating the  feed  and  heat,  for  the  removal  of  the  roasted 
ore,  the  inspection  of  the  interior,  and  the  admission  of 
air  at  suitable  points,  and  in  proper  quantity. 

In  a  large  furnace,  capable  of  roasting  from  30  to  70 
tons  of  ore  in  24  hours,  the  roasting  tower  is  25  feet 
high  and  five  feet  square  at  the  base.  One  man  on  a 
shift  can  attend  to  the  firing. 

The  following  extract  from  the  Circular  of  the  Stete- 
feldt  Furnace  Co.  will  assist,  with  the  drawings^to  an 
understanding  of  the  arrangement : 


158  ADDENDA. 

"  Of  the  accompanying  drawings  Figure  i  represents 
a  vertical  section  of  the  Stetefeldt  Furnace,  showing 
its  latest  and  most  improvd  mode  of  construction,  and 
Figure  2  is  a  sketch  of  the  Stetefeldt  Feeder. 

DESCRIPTION    OF    THE    FURNACE. 

A  is  the  shaft  into  which  the  pulverized  ore  is 
showered  by  the  feeding  machine,  placed  on  the  top  of 
the  cast  iron  frame  B.  The  shaft  is  heated  by  two 
fireplaces  (C).  The  ashpits  of  these  are  closed  by  iron 
doors,  having  an  opening  (E),  provided  with  a  slide, 
so  that  more  or  less  air  can  be  admitted  below  the 
grate,  and,  consequently,  more  or  less  heat  generated. 
In  order  to  obtain  a  perfect  combustion  of  the  gases, 
leaving  the  firebox  through  the  slit  (T),  an  airslit  (U), 
connected  with  the  airchannel  (F),  is  arranged  above 
the  arch  of  the  firebox.  This  slit  also  supplies  the  air 
necessary  for  the  oxidation  of  the  sulphur  and  the  base 
metals.  Another  advantage  of  this  construction  is  that 
the  arches  above  the  firebox  and  firebridge  are  cooled 
and  prevented  from  burning  out.  The  roasted  ore  ac- 
mulates  in  the  hopper  (K),  and  is  discharged  into  an 
iron  car  by  pulling  the  damper  (L),  which  rests  on 
brackets  with  friction  rollers  (M).  N  is  an  observation 
door,  and  also  serves  for  cleaning  the  firebridges.  O 
are  doors  to  admit  tools  in  case  the  roasted  ore  is  sticky 
and  adheres  to  the  walls.  The  gases  and  fine  ore  dust, 
which  forms  a  considerable  portion  of  the  charge,  leave 
the  shaft  through  the  flue  (G).  The  doors  (R)  are  pro- 
vided to  clean  this  flue,  which  is  necessary,  with  some 
ores,  about  once  a  month.  D  is  an  auxiliary  fireplace, 
constructed  in  the  same  manner  as  the  fireplaces  on 


Fisf.l. 


THE  STETEFELDT  FURNACE . 


ADDENDA.  159 

the  shaft,  which  is  provided  to  roast  the  ore  dust,  escap- 
ing through  the  flue  (G),  in  passing  through  the  cham- 
ber (H).  P  are  doors  for  observation  and  cleaning. 
The  larger  portion  of  the  roasted  dust  settles  in  the 
chamber  (V).  provided  with  discharge  hoppers  (I), 
from  which  the  charge  is  drawn  into  iron  cars  by  moving 
the  dampers  (S).  The  rest  of  the  dust  is  collected  in  a 
system  of  dust  chambers  (O),  connected  with  a  chimney 
which  should  rise  from  40  to  50  feet  above  the  top  of 
the  shaft.  At  the  end  of  the  dust  chambers  is  a  damper 
by  which  the  draft  of  the  furnace  can  be  regulated. 
The  dry  kiln  can  also  be  used  as  a  dust  chamber,  and 
the  waste  heat  of  the  furnace  utilized  for  drying  the  ore 
before  crushing  it.  The  firing  of  the  furnace  is  done 
on  one  side,  and  all  discharges  are  located  on  the  op- 
posite side." 

DESCRIPTION    OF    THE    FEEDING    MACHINE. 

"  The  Feeding  Machine  is  shown  in  Fig.  2.  The 
castiron  frame  (A),  which  is  placed  on  top  of  the  shaft, 
is  'provided  with  a  damper  (B),  which  is  drawn  out 
when  the  furnace  is  in  operation,  but  inserted  when  the 
feeding  machine  stops  for  any  length  of  time,  or  if 
screens  have  to  be  replaced.  C  is  a  castiron  grate,  to 
the  top  of  which  is  fastened  the  punched  screen  (D). 
The  latter,  is  made  of  Russian  sheetiron,  or  of  cast-steel 
plate,  with  holes  of  one-eighth  to  one-tenth  of  an  inch 
in  diameter.  Above  the  punched  screen  is  placed 
a  frame  (B),  to  the  bottom  of  which  is  fastened 
a  coarse  wire  screen  (F),  generally  No.  3,  made  of  extra 
heavy  iron  wire.  The  frame  (E)  rests  upon  friction 
rollers  (G).  The  brackets  (H)  which  hold  the  friction 


160  ADDENDA. 

rollers  can  be  raised  or  lowered  by  set  screws,  so  that 
the  wire  screen  (F)  can  be  brought  more  or  less 
close  to  the  punched  screen  (D).  The  brackets 
(K)  carry  an  eccentric  shaft  (L),  connected  with 
the  shaft  (M),  from  which  the  frame  (E)  receives 
an  oscillating  motion.  To  the  brackets  (N)  are 
fastened  transverse  stationary  blades  (O),  which 
come  nearly  in  contact  with  the  wire  screen  (F),. 
and  can  be  raised  or  lowered  by  the  nuts  (P).  These 
blades  keep  the  pulp  in  place  when  the  frame  (E)  is  in 
motion,  and  also  act  as  distributors  of  the  pulp  over 
the  whole  surface  of  the  screen.  The  hopper  (I)  re- 
ceives the  ore  from  an  elevator  which  draws  its  supply 
from  a  hopper  into  which  the  pulverized  ore  is  dis- 
charged from  the  crushing  machinery.  The  ore  is  gen- 
erally pulverized  through  a  No  40  screen.  By  means 
of  a  set  of  cone  pulleys  the  speed  of  the  frame  (E)  can 
be  changed  from  twenty  to  sixty  strokes  per  minute,, 
whereby  the  amount  of  ore  fed  into  the  furnace  is  regu- 
lated. This  can  also  be  done  to  some  extent,  by 
changing  the  distances  between  the  punched  screen 
(D),  the  wire  screen  (F),  and  the  blades  (O). 

The  largest  sized  furnace,  as  represented  in  the  draw- 
ing— the  scale  of  which  is  i  in.  =  12  ft.,  capable  of 
roasting  from  50  to  70  tons  of  ordinary  ores,  and  from 
30  to  35  tons  of  very  base  sulphuret  ores  in  24  hours, 
requires  the  following  amount  of  materials,  from  which, 
the  cost  of  construction  can  be  easily  calculated  by  any 
architect  or  millwright,  viz: 

1,500  fire-bricks,  for  fire  boxes  and  arches  exposed  to> 
flame. 


ADDENDA.  161 


200,000   common   bricks,   of  good  quality,  for  furnace, 
large  system   of  dust  chambers,  chimney,    and 
cooling  floor. 
2,500  Ibs.  'in  bolts  and  nuts   for  anchoring  furnace  and 

dust  chambers. 

4,500  Ibs.    in   wrought  iron  braces,  flat   iron  for  car- 
guides,  tools,  etc. 
16,000  Ibs.  in  castings. 

All  the  castings  are  very  plain  and  simple,  the  water- 
jacket  on  top  of  furnace,  and  the  water  damper  having 
been  discarded.  Considerable  work  is  only  required 
on  the  feeding-machine,  feeding-machine  damper,  and 
•  discharge  damper,  and  some  on  the  fire-doors,  which 
will  be  covered  by  an  additional  charge  of  about  $700 
added  to  the  ordinary  price  of  castings. 

The  cost  of  three  iron  discharge  cars  is  $125. 
For  a  furnace  of  15  to  20  tons  capacity,  without  hopper 
.discharge,  and  a  less  extensive  system  of  dust  cham- 
bers, the  amount  of  materials  required  may  be  esti- 
mated 'at  two-thirds  the  figures  given  above." 


REMARKS  ON  FURNACES. 

214.  The  quantity  of  fuel  consumed  in  roasting 
varies  with  the  quality  of  the  fuel,  the  character  of  the 
•ore,  and  the  kind  of  furnace  used. 

In  a  single  hearth  reverberatory  furnace,  each  ton  of 
ordinary  silver  ore  requires   from    one-third  to  one-half 
.a  cord  of  dry  pine  wood.      In   a   long  furnace  the  pro- 
portion is  materially  reduced. 


162  ADDENDA. 

Concentrated  auriferous  sulphides,  when  roasted  for 
chlorination,  in  a  reverberatory  furnace  with  three 
hearths,  require  one  cord  of  wood,  or  one-half  ton  of 
Seattle  coal,  per  ton  of  ore.  In  this  roasting,  one  man 
on  a  shift  is  sufficient  for  one  furnace,  roasting  i  ^ 
tons  of  ore  in  each  24  hours.  The  writer  experimented 
with  different  numbers  of  men  employed  at  one  time, 
but  found  no  advantage  in  more  than  one  for  all  three 
hearths,  thus  proving  that  stirring  the  ore  beyond  a 
certain  extent  is  useless,  unless  the  supply  of  air  be  in- 
creased. In  the  mechanical  furnaces  the  proportionate 
consumption  of  fuel  is  much  dimished,  especially  in 
those  which  receive  the  ore  continuously,  in  which  one- 
tenth  of  a  cord  of  wood  to  the  ton  of  silver  ore  is  a 
common  proportion.  The  mechanical  furnaces  de- 
scribed are  all  in  more  or  less  extensive  use,  giving 
satisfactory  results,  with  great  economy  of  fuel  and 
labor  as  compared  with  the  old  reverberatory  furnace. 

Those  which  receive  the  ore  continuously  are  the 
most  economical  in  operation,  but  the  most  costly  in 
construction.  They  are  especially  adapted  to  the  chlo- 
ridizing  roasting  of  large  quantities  of  silver  ore  of 
nearly  uniform  character. 

For  the  roasting  of  gold-bearing  sulphides,  or  excep- 
tionally rich  silver  ores,  for  custom  works  in  which  the 
character  of  different  small  lots  of  ore  is  liable  to  ex- 
treme variation,  or  in  small  establishments,  the  furnaces, 
which  are  charged  periodically  are  usually  preferred,  be- 
cause the  roasting  in  them  is  more  readily  controlled, 
or  because  of  their  more  moderate  cost. 

The  furnaces  which  are  charged  continuously,  as  the. 


ADDENDA.  163 

Stetefeldt,  and  the  White  with  its  modifications,  have 
not  yet  been  tried  for  the  dead  roasting  of  gold-bearing 
sulphurets  for  the  Plattner  process,  but  there  is  no  rea- 
son to  dcrubt  that,  with  proper  care,  they  might  be 
made  to  do  the  work.  Possibly  a  modification,  such  as 
that  used  by  Mr.  Crosby  (50)  in  connection  with  his 
reverberatory  furnace,  might  be  necessary  on  account  of 
the  large  quantity  of  sulphur  which  the  material  in 
question  contains. 

One  disadvantage  of  the  continuous  cylinder  furnaces 
in  which  the  ore  progresses  in  an  opposite  direction 
to  the  draft  is,  that  the  heavier  particles,  which  require 
the  longest  exposure,  pass  through  more  quickly  than 
the  lighter,  because  the  force  of  the  draft  has  less  influ- 
ence in  retarding  their  horizontal  progression.  The 
action  of  the  furnace  must  be  adjusted  to  the  require- 
ments of  these  heavy  particles.  Between  these  and 
the  dust  which  is  completely  controlled  by  the  draft, 
are  particles  of  all  grades,  some  of  which  are  barely 
massive  enough  to  make  headway  against  the  current 
of  air. 

As  the  time  required  for  the  roasting  of  the  larger 
particles  is  greater  than  that  required  for  the  smaller,  it 
is  clear  that  a  large  proportion  of  the  ore  which  passes 
through  the  cylinder  is  detained  within  it  longer  than 
is  necessary,  causing  useless  consumption  of  power  and, 
in  all  probability,  loss  of  silver.  This  defect  is  obvi- 
ated when  the  ore  moves  through  the  furnace  in  the 
same  direction  as  the  draft.  The  progression  of  the 
ore  is  then  aided  by  the  force  of  the  draft,  but  in  a  less 
degree  as  the  particles  are  heavier.  The  objection  to 
this  method  is,  that  the  ore  in  its  progress  encounters  a 


164  ADDENDA. 

gradually  diminishing  heat,  and  a  decreased  proportion 
of  oxygen,  while  the  reverse  should  be  the  case. 

Mr.  White,  the  original  inventor  of  the  application 
of  this  kind  of  furnace  to  the  treatment  of  silver  ores, 
has  been  much  blamed  for  his  persistence  in  this  man- 
ner of  working  it,  but  it  must  be  admitted  that,  if  the 
objection  pointed  out  could  be  overcome,  the  method 
would  possess  certain  advantages. 

In  the  Stetefeldt  furnace,  in  like  manner,  the  descent 
of  the  heavier  particles  is  less  impeded  by  the  upward 
current  of  air  and  gas,  and  is  therefore  more  rapid  than 
that  of  the  lighter,  but  in  this  case  no  waste  of  power 
results,  because  the  ore  is  lifted,  once  for  all,  to  the  top 
of  the  shaft  by  an  elevator. 

In  the  O'Hara,  all  portions  of  the  ore,  except  a  small 
quantity  of  very  light  dust,  are  moved  toward  the  hot- 
ter end  of  the  furnace  with  practical  uniformity.  This 
furnace  combines  the  advantages  of  the  reverberatory, 
worked  by  hand,  with  those  of  automatic  action.  It 
probably  costs  more  for  repairs  than  the  others. 

A  roasting  furnace,  of  whatever  description,  should 
be  kept  in  operation  as  constantly  as  possible,  not  only 
in  order  to  economize  fuel,  but  also  to  avoid  the  injuri- 
ous effect  of  alternate  heating  and  cooling.  In  the  se- 
lection, therefore,  regard  should  be  paid  to  the  quantity 
of  ore  to  be  treated  daily,  as  well  as  to  its  character,  and 
the  financial  resources  at  command. 


INDEX'. 


PAGE.  PAR 

Absorbed  Gold  —  recovery  of 107  17 

Acid— cost  of .   ...110  18( 

Action  of  chlorine_on  oil 40  6 

Alloy  of  gold  and  silver 82  14 

Ammonia — use  of , 49  92 

Antimony    and  arsenic— behavior  of 

in  roasting 16-19  18-29 

Apparatus 22  33 

Assay  of  concentrations 97  158 

boiling  over  of 101  164 

methods  of 93  159 

1st 99  160 

2d 100  161 

3d 100  162 

4th 102  165 

5th 102  166 

6th 103  168 

Assay — chlorination,  the  so-called 132  200 

"      copper  ores,  &c.,  of — for  gold 

and  silver 103  167 

"      manganese  of 114  184 

rich  silver    ore   of  —  precau- 
tion in 104  170 

"      salt  of 112  182 

•"      silver  glance  of 104  '. 

"      solubility,  the  93  156 

"      tailingsof  104  171 

Bar,  gold— casting  the 64  117 

Bar,  silver        "        "    73  135 

Bars— value  of 137  202 

Bo,  tie- wash— see  wash -bottle 

Bruckner  furnace,  the 143  206 

Brunton  furnace,  the 145  207 

Calcium  polysulphide 83  148 

use  of 70  129 

test  for  excess  of 71  130 

Calcium  hyposulphite 85  150 

proper  strength  of. 85  151 

Cement-copper—assay  of  for  gold  and 

silver 103  167 

Chemical  combination 10  7 

Chlorine 138  203 

action  of  on  oil f 40  69 

expelling  of  by  steam 118  186 

excess  of 54  97 

disposal  of 56  98 

source  of 12  10 

surplus 117  ige 

Chlorine  generator 37  65 

charging  the 51  94 

discharging  the 52  95 

description  of 37  67 


PAOK. 

joints  of 37 


PAR. 


Chloride — metal 12  10 

how  formed  in  roasting 17  21 

Chloride  -silver  — how    formed    for 

leaching 12  13 

volatilization  of 19  32 

Chlorides  —  base  —  action  of  in  roast- 
ing...  : 18  24 

Chloridizing  roast 17  20 

Chlorination  of  gold  ore 49  92 

Chlorination    assay  —  so-called  —  not 

correct 132  200 

Chlorination  Tailings 135  201 

Chlorinating  (leaching)  vat 31  51 

charging  the 48  90 

Chamber— drying— for  gold,  &c 121  192 

Change  in  weight  of  ore  in  roasting  .  91  154 

Clay  and  talc  in  unconcentrated  ore  80  144 

Combination— chemical 10  7 

Concentrated  pyrites  containing  gold, 

but  not  silver 41  71 

charge  of,  proper 42  75 

how  kept 41  72 

lime  or  talc  in 41  73 

roasted,  chlorination  of 49  92 

examination  of 46  86 

leaching  of 53  96 

moistening  of , 48  89 

roasting  of 43  77 

heat  for 47  87 

time  of 47  88 

stirring  of  in  roasting 43-45  78-81 

Concentrated     pyrites      containing 

gold  and  silver 65  118 

leaching  of  for  gold 66  122 

for  silver 67  123 

roasting  of 65  119 

loss  in  to  prevent 65  120 

Concentrations  containing  silver,  but 

little  or  no  gold 75  136 

roasting  of 75  137 

loss  in  to  prevent 76  138 

washing  of 77  139 

leaching,  &c.,  of 79  141 

oncentrations      containing     much 

lead,  &c.,  Hof man's  process 79  142 

Concentrations  —  assaying  —  see  as- 
saying concentrations 

Copper— saving 106  174 

assay  of  for  gold  and  silver 103  167 

chloride,  action  of  in  roasting 18  26 

sulphate — test  for : - 46  84 

Cost  of  acid no  180 


166 


INDEX. 


PAGE.  PAR. 

Covering-flue 105  172 

Crosby's  furnace 30  50 

Dead  roast 16  19 

Directions — special  -for  working 41  71 

Drier— ore 27  44 

for  precipitate 28  45 

Drying  the  gold 62  110 

Drying  chamber 121  192 

Dust  chamber 27  44 

Dumping  vats 32  52 

Filter  in  leaching  vat 32  53 

drying  the 48  90 

in  dumping  vat 105  173 

Filters  for  precipitates 36  62 

Filtration 9  2 

Flowing  (in  leaching) 9 

Flue  covering 105  172 

Fuel  for  melting 62  135 

roasting 22  34 

quantity  required.  .161  214 

Furnace— Bruckner,  the 143  206 

Brunton,  the 145  207 

Crosby's 30  50 

Howell  White,  the 147  210 

melting  for  bullion 128  198 

O'Hara,  the 155  212 

Pacific  chloridizing,  the 145  208 

reverberatory 22  34 

charge  for 42  75 

construction  of 22  36 

the  arch 25  41 

doors 25  40 

door  frames 24  39 

fire  place '...  27  42 

stack .....27  43 

walls 23  37 

drying  of 41  74 

innovations  in 28  46 

kinds  of 22  35 

roasting,  for  silver  precipitate 28  45 

step 29  47 

Stetefeldt,  the 156  213 

Thompson  White,  the 148  211 

White,  the 146  209 

Furnace  tools 30  49 

Furnaces—roasting— remarks  on 161  214 

Generator — chlorine 37  65 

different  forms  of 108  177 

Gold  -absorbed — recovery  of 107  176 

behavior  of  in  roasting 16-19   18-30 

bar — casting  the 64  117 

cleaning  the  melted 64  116 

coarse,  or  alloyed  with  silver 82  146 


PAGE,  PAR. 

collecting  the 60  108 

drying  the 62  110 

extracted  from  ores— how 9  0 

f iltei  for  precipitated 36  62 

leaching  of 53  96 

loss  of  in  roasting— to  prevent 65  120 

melting  the 62  111 

sand  in 120  191 

precipitating  the 57-118  100-187 

precipitants  for  —  see  precipitanta 
for  gold 

settling  of 59  104 

solution— color  of 57  99 

impurities  in 118  188 

suspended  (in  waste  liquid) 119  18!) 

terchloride 12  11 

test  for  in  leach 57  101 

volatilization  of 121  193 

Gold  tub— discharge  of 60  107 

Hoe — stirring 30  49 

Hofman's  process 79  142 

Howell  White  furnace,  the 147  210 

Hypo — pipes  and  faucets  for 37  64 

Hyposulphite — calcium 85  150 

solution,  strength  of 85  151 

sodium 131  199 

Introduction 9 

Iron    perchloride — behavior     of    in 

roasting 18  25 

Iron  sulphate  solution 59  106 

Iron — use  of  in  melting  silver 12  13 

Kiss  process,  the 142  205 

Leach— leaching,  lixivium,  lixiviation    9  1 

Leaching— difficulty  in 80  144 

mode  of— for  gold  and  silver 9  5 

Leaching  gold  ore 53  96 

silver 67  123 

time  required  for 70  128 

Leaching  vat 31  51 

Lead  chloride — to  remove 78  140 

in  gold  solution 118  1SS 

Lead  in  ore— why  troublesome 19  31 

Lead  sulphate— action  of  in  roasting.  18  27 

Leaks  of  chlorine 50  93 

Loss  in  roasting — to  ascertain 92  155 

Manganese— and  salt,  proportions  of.  116  185 

assay  of 114  184 

Matte  from  silver  melting 127  197 

Mears  process 83  147 

Melting  furnace 128  198 

Metal— chlorides 12  10 

in  the  furnace — how  formed 17  21 

action  of  18  24 

Metal— oxides,  sulphide,  sulphate...  15  15 


INDEX. 


107 


PAGE  PAR. 

Melting  the  gold 62  111 

use  of  sand  in 120  191 

O'Hara  furnace,  the 155  212 

Oil -action  of  chlorine  on— use  of....  40  69 

Ores — containing  coarse  gold 82  146 

how  leached  for  gold  and  silver 9  5 

leached — scum  on 72  131 

preparation  of  for  roasting 15  17 

roasted— chamber  for 29  48 

sifting  of 110  179 

sieve  for 34  56 

washing  of 77  139 

unconcentrated— treatment  of 80  143 

clay  and  talc  in 80  144 

Oxide— metal 15  15 

Oxidizing  roast 16  18 

Pacific  chloridizing  furnace,  the 146  208 

Percolation — unequal 68  102 

Pipe— suction 32  64 

to  use 81  145 

vent 33  55 

Pipes  and  faucets  for  hypo 37  64 

Plan  of  works 94  157 

Plattner's  process 140  204 

(   12  11 

Precipitants  for  gold •!    83  146 

( 119  190 

Precipitants  for  silver 70-83    129-146 

Precipitate — silver — collecting  the 73  133 

dryer  for  the 28  45 

melting  the ?S  135 

roasting  the 73  134 

'   fu  nace  for 28  45 

Precipitating  gold. 57-118    100-187 

Precipitating  vat  35-117    57-18? 

means  of  drawing  liquid  from 106  175 

Precipitation— exp'anation  of 11  9 

of  Silver 70  129 

of  weak  solutions— gold 59  105 

silver 72  132 

Preface 5 

Press— for  precipitate 37  63 

Process— Hof man's 79  142 

Kiss,  the 142  205 

Mears,  the 83  147 

Plattner's 140  204 

Pumps 36  61 

Pyrites — concentrated  —  see   concen- 
trated pyrites 

Recovery  of  sulphur 126  196 

Remarks  on  furnaces  (roasting). .     . .  161  214 
Reverberatory   furnace — see  furnace 

reverberator}' 


TACK.  PAR. 

Roast— chloridizing 17  20 

dead 16  19 

oxidizing 16  18 

Roasting  ores— effect  and  purpose  of.  15  16 

loss  in  to  ascertain 92  155 

Roasting  furnaces 21  33 

Salt — action  of  in  roasting 17  21 

assay  of 112  182 

and  manganese — proportions  of...  116  185 

composition  of 17  21 

purification  of 114  183 

(   17  21 

use  of  in  roasting -    41  73 

(   65  120 

Sand  in  gold  melting 120  191 

in  silver  melting. 131  198 

Scorification  assay 103  168 

Scum  on  leached  ore 72  131 

Sieve  for  ore • 34  66 

Sifting  ore 110  179 

Silver  chloride— how  made  for  leach- 
ing   12  13 

volatilization  of  19  32 

to  prevent 76  138 

Silver- extracted  from  ores— how....     9  6 

leaching  the 67  123 

time  required  for 70  128 

precipitation  of  the 70  129 

precipitate— collecting  the 73  133 

"          dryer  for    28  45 

filters  for 36  62 

"         matte  from 127  197 

melting  the 73  135 

"          roasting  the 73  134 

roasting  for 65-75  119-137 

solution  of  in  hypo 124  194 

test  for  in  leach 68  125 

Silver  glance— assay  of 104  169 

Silver  ore— rich— assay   of — precau- 
tion in 104  170 

Silver  ore — roasted— washing  the ...   77  139 

Sodium  hyposulphite 131  199 

Solution 10  8 

iron  sulphate 59  106 

gold  chloride— color  of 57  99 

of  silver  in  hypo 124  194 

Solubility   assay  ("chlorination    as- 
say")  - 93  156 

Steam— effect  of  in  roasting 17  23 

use  of  to  expel  chlorine 118  186 

Step  furnace 29  47 

Stetefeldt  furnace,  the 156  213 

Suction  pipe , 32  54 


168 


INDEX. 


PAGE.  PAR. 

to  use 81  145 

Sulphates— metal— action  of  in  roast- 
ing  16-17  19-21 

Sulphate— lead  action   of   in    roast- 
ing   18  27 

Sulphide  (sulphuret)  metal 15  15 

Sulphur— recovery  of.....' 126  196 

waste  of 125  195 

Sulphur  oxide  —  effect  of  in  roast- 
ing  7-17  22 

Sulphurets  concentrated  —  see  con- 
centrated pyrites 

Surplus  chlorine 54-117  97-186 

Suspended  gold  (in  waste  liquid) 119  189 

Tailings— assay  of 104  171 

chlorination 135  201 

Test  for  calcium  sulphide 71  130 

"      chlorine 49  92 

"      copper  sulphate  (in  ore). ..  46  84 

"      gold  in  leach 57  101 

"      hypo— strength  of 85  151 

"      iron  sulphate  (in  ore) 45  83 

silver  in  leach 68  125 

Test-working 86  152 

a  smaller 90  153 

Thompson  White  furnace,  the 148  211 

Tools— furnace 30  49 

Troughs  for  solutions 36  59 

arrangement  of 67  123 

Tub-wash—see  wash-tub . . . 


PA6K.  PAR. 

Unconcentrated  ore— treatment  of.. .  80  143 

Unequal  percolation 58  102 

Value  of  bars 137  202 

Vat— calcium  polysulphide 36  58- 

charging  the— for  chlorination 48  90 

chlorination— see    rat-leaching.  .. 

dumping 32  52 

filter  in 105  173 

iron  sulphate 35  58 

leaching 31  51 

precipitating  —  see     precipitating 

vat 

Vent  pipe 33  55 

Volatilization  of  gold 121  193 

"             silver  chloride 19  32 

Wash  bottle 39  68 

uses  of 40  70 

forms  of 108  178 

Washing  the  gold 61  109 

silver  ore  (roasted)  77  139 

Waste  of  sulphur 125  195 

Weak  solution— gold 59  105 

"              silver 72  132 

Weight—  change  in  (in  roasting  ore). .  91  154 

Well— for  hypo 36  60 

White  furnace,  the 146  209 

Working — special  directions  for 41  71 

Working  test 86  152 

a  smaller 90  153 

Zinc— behavior  of  in  roasting 17-21  18-28 


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AW    12   1932 

JAN  03 '91 


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SEP  14 1993 


757n-8,'31 


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r    •• 


